Been messing around with fun casual decks on DN recently. Can't be bothered with sideboards etc, since most of the games I do are one-offs.
Blue-Eyes themed deck based around MASSIVE DRAW POWER. Strategy: use the 22 card drawing/adding cards to draw through the entire deck, then OTK with three Blasting the Ruins. Blue-Eyes never gets to battle, just being discarded/tributed to draw cards whenever I can.
I have Cards of Consonance to discard The White Stone of Legend (and draw two cards). Then, I can use Trade In to send the Blue-Eyes White Dragon I fetched to the graveyard (and draw two cards). I resurrect it with any of the seven resurrection spells/traps, and immediately tribute it again for Advance Draw (and draw two cards) or send it to the graveyard for White Elephant's Gift (and draw two cards). Of course, I have Card Destruction and Morphing Jar to fill up my graveyard and burrow even faster through the deck; I've had times where Card Destructions got me 9 cards. Obviously, this means I'm discarding and tributing White Stone and Blue-Eyes constantly - Super Rejuvenation turns each of these into yet more cards. Reckless Greed lets me get going faster, and can be reused with Mask/Trap of Darkness. Mask/Trap of Darkness are in there mainly to get back Blasting the Ruins if it's destroyed; Trap has the advantage of being able to get around the 30-card restriction, though thanks to its 1000LP cost and 3000LP maximum requirement, it's not enough to win by itself.
I've had many situations where I end up drawing through the entire deck; I usually have to get down to my last couple of cards before my graveyard is full enough to activate Blasting the Ruins. Opponent thinks I'm screwed, and passes the turn to force me to draw from my empty deck... only to be greeted with 9000LP damage as I'm about to lose. Fun stuff.
I have to give credit to my little brother who came up with this deck; I just tweaked it to make it a bit more reliable.
Things it auto-loses to: Macro Cosmos, Royal Decree, anything really fast that can kill me before I draw into the combo.
The Aesir are the kind of big, flashy card I like. Once one's up, it's pretty difficult to get rid of with their negation and resurrection effects. And getting more than one means the opponent is going down fast.
Nordics are pretty good at searching each other out and getting up materials for the Aesir; Valkyrie of the Nordic Ascendant is a good opener or last resort, getting me Odin, Father of the Aesir in exchange for two Nordics from my hand. Its condition is pretty restrictive; Vanadis of the Nordic Ascendant gives me access to Odin (or either of the other two) once I have board presence. Mara of the Nordic Alfar is useful for instant Loki, Lord of the Aesir; I can use two of either Tyr of the Nordic Champions or Garmr of the Nordic Beasts from my hand to summon him, or the goats for level 8 Synchros. Speaking of the goats, Tanngrisnir of the Nordic Beasts and Tanngnjostr of the Nordic Beasts combo pretty well; open with a face-down Tanngrisnir, let the opponent kill it and summon Tanngnjostr, then next turn use Tanngnjostr to search out Guldfaxe of the Nordic Beasts and make Thor, Lord of the Aesir. Gleipnir, Fetters of Fenrir makes it easy to get the Nordics I need, and Loki helps to reuse it. Vanadis dumps Nordic Tuners to the graveyard to keep the Aesir alive, as well as being pretty easy to use for Synchros thanks to its level-changing power. March Towards Ragnarok is a bit situational, but it's definitely had its moments - for example, it stops stray Bottomless Trap Holes destroying my hard work, and gives the Aesir protection during my opponent's turn. Sangan gives more searching power, and Black Luster Soldier - Envoy of the Beginning is just amazing (though it interferes with the Aesir's resurrection effects). There's a couple of traps to deal with pesky effect monsters that aren't negated by March Towards Ragnarok or Loki/Odin - in contrast to spells/traps, monsters are most often used in my opponent's turn, so Thor's negation effect isn't nearly as useful.
It's a bit of a non-traditional Synchro-based deck, but it's surprisingly effective - the Synchros it makes are more powerful and durable than the likes of Stardust Dragon, making up for their steeper requirements.
I just beat a Dragunity player in an excellent game; I got Loki up relatively early to counter the Stardust Dragon my opponent summoned on his first turn - his Gozen Match stopped me playing it earlier, as I had a spare Nordic Beast token still on the field. He destroyed it, then Bottomless Trap Holed its resurrection (I didn't have March Towards Ragnarok at this point); I followed up with Black Luster Soldier, which took out a massive chunk of his LP before falling to Gae Bulg. Black Luster Soldier being down meant I could summon Mara (Gozen Match was still up), then tune it with Tanngrisnir and Tanngnjostr in my hand for Scrap Dragon and game. Good stuff.
I've been tempted to start buying physical cards again, but I've resisted so far. The Aesir deck (minus BLS) and two Fairy decks I made earlier are actually really cheap to construct, coming out to ~$20 per deck (one of them is only $10 - most of the cards were in the recent structure deck!). But then there's shipping to the UK, which is a pain. And I bought the 2011 DS game to avoid having to buy cards - it doesn't seem to be working :/
EDIT: Aesir deck price doesn't include non-Aesir Synchros/Xyz. I don't use them that much anyway.

Blue-Eyes themed deck based around MASSIVE DRAW POWER. Strategy: use the 22 card drawing/adding cards to draw through the entire deck, then OTK with three Blasting the Ruins. Blue-Eyes never gets to battle, just being discarded/tributed to draw cards whenever I can.
I have Cards of Consonance to discard The White Stone of Legend (and draw two cards). Then, I can use Trade In to send the Blue-Eyes White Dragon I fetched to the graveyard (and draw two cards). I resurrect it with any of the seven resurrection spells/traps, and immediately tribute it again for Advance Draw (and draw two cards) or send it to the graveyard for White Elephant's Gift (and draw two cards). Of course, I have Card Destruction and Morphing Jar to fill up my graveyard and burrow even faster through the deck; I've had times where Card Destructions got me 9 cards. Obviously, this means I'm discarding and tributing White Stone and Blue-Eyes constantly - Super Rejuvenation turns each of these into yet more cards. Reckless Greed lets me get going faster, and can be reused with Mask/Trap of Darkness. Mask/Trap of Darkness are in there mainly to get back Blasting the Ruins if it's destroyed; Trap has the advantage of being able to get around the 30-card restriction, though thanks to its 1000LP cost and 3000LP maximum requirement, it's not enough to win by itself.
I've had many situations where I end up drawing through the entire deck; I usually have to get down to my last couple of cards before my graveyard is full enough to activate Blasting the Ruins. Opponent thinks I'm screwed, and passes the turn to force me to draw from my empty deck... only to be greeted with 9000LP damage as I'm about to lose. Fun stuff.
I have to give credit to my little brother who came up with this deck; I just tweaked it to make it a bit more reliable.
Things it auto-loses to: Macro Cosmos, Royal Decree, anything really fast that can kill me before I draw into the combo.

The Aesir are the kind of big, flashy card I like. Once one's up, it's pretty difficult to get rid of with their negation and resurrection effects. And getting more than one means the opponent is going down fast.
Nordics are pretty good at searching each other out and getting up materials for the Aesir; Valkyrie of the Nordic Ascendant is a good opener or last resort, getting me Odin, Father of the Aesir in exchange for two Nordics from my hand. Its condition is pretty restrictive; Vanadis of the Nordic Ascendant gives me access to Odin (or either of the other two) once I have board presence. Mara of the Nordic Alfar is useful for instant Loki, Lord of the Aesir; I can use two of either Tyr of the Nordic Champions or Garmr of the Nordic Beasts from my hand to summon him, or the goats for level 8 Synchros. Speaking of the goats, Tanngrisnir of the Nordic Beasts and Tanngnjostr of the Nordic Beasts combo pretty well; open with a face-down Tanngrisnir, let the opponent kill it and summon Tanngnjostr, then next turn use Tanngnjostr to search out Guldfaxe of the Nordic Beasts and make Thor, Lord of the Aesir. Gleipnir, Fetters of Fenrir makes it easy to get the Nordics I need, and Loki helps to reuse it. Vanadis dumps Nordic Tuners to the graveyard to keep the Aesir alive, as well as being pretty easy to use for Synchros thanks to its level-changing power. March Towards Ragnarok is a bit situational, but it's definitely had its moments - for example, it stops stray Bottomless Trap Holes destroying my hard work, and gives the Aesir protection during my opponent's turn. Sangan gives more searching power, and Black Luster Soldier - Envoy of the Beginning is just amazing (though it interferes with the Aesir's resurrection effects). There's a couple of traps to deal with pesky effect monsters that aren't negated by March Towards Ragnarok or Loki/Odin - in contrast to spells/traps, monsters are most often used in my opponent's turn, so Thor's negation effect isn't nearly as useful.
It's a bit of a non-traditional Synchro-based deck, but it's surprisingly effective - the Synchros it makes are more powerful and durable than the likes of Stardust Dragon, making up for their steeper requirements.
I just beat a Dragunity player in an excellent game; I got Loki up relatively early to counter the Stardust Dragon my opponent summoned on his first turn - his Gozen Match stopped me playing it earlier, as I had a spare Nordic Beast token still on the field. He destroyed it, then Bottomless Trap Holed its resurrection (I didn't have March Towards Ragnarok at this point); I followed up with Black Luster Soldier, which took out a massive chunk of his LP before falling to Gae Bulg. Black Luster Soldier being down meant I could summon Mara (Gozen Match was still up), then tune it with Tanngrisnir and Tanngnjostr in my hand for Scrap Dragon and game. Good stuff.
EDIT: Aesir deck price doesn't include non-Aesir Synchros/Xyz. I don't use them that much anyway.