http://www.youtube.com/watch?v=H9tL1p9YbGk (Dialga/Palkia Battle from SSBB).
This one is not *directly* from a Pokémon game, but a Pokémon tune regardless. Simply the best of D/P music. Starts with the thundering piano, then continues with the "hammer meets anvil" bass while the piano continues to chunk out that bizarre, yet epic tune. I learned it on piano once, but have forgot most of it since.
Also trying to explain my disdain for D/P music. Take, as an example, Route 205, the example MWL posted.
The first ten seconds are skippy and country-like, as if something festive is going on (rodeo, race, general yee-haw).
Then follow twenty seconds of calm piano and harmonica. Generic route/town music.
Then a ten-second bridge, which neither follows the speed nor the melody of the previous part of the song...
...into another skippy, upbeat part which sort of follows the beginning. But the entire song is entirely without coherence, the melody easy to forget. What is this theme supposed to convey? Randomness? Generic "now we are in Sinnoh" feeling? All the route/town themes feel like this. None of them sets you in any special mood, it's all just "OK, here we are. This is the background music. It's only here because silence would be weirder."
Contrast, for instance, Route 201. It begins with a couple of measures leading up to an ear-worm of a melody, which then repeats at a sensible point. The song just feels like it belongs early in the adventure. The humble beginning. It's full of the naïve sense of adventure from early-game, before you learn that something is wrong in Sinnoh.
Or, take Route 11 from Gen. I.
http://www.youtube.com/watch?v=7bRctqZpTM8
Picture the rolling plains in Southern Kanto. Tall grass from horizon to horizon, a breeze from the ocean rustling the entire plain. The sun is shining, Pidgey are singing, and in the distance you can see a flock of Ponyta running along the border fence of the Safari Zone. It's one of those days that make you feel that everything up till now was worth it, just for standing here and looking at the plain. The very picture you had in your head when you decided to set out on your journey. The very sensation of being a trainer.
This song has a clear and distinct context: Wide-open, optimistic epicness. It's 8-bit, yet you can imagine the trumpets and strings as clear as day. Listen to the
Pokémon Stadium version of the theme. Clear use of instruments. The song has an easy melody despite being orchestrated.
Another example:
Route 216. What is this mess? Where are we supposed to be? What happens at 0:44? What is this song supposed to depict? The choice of instrument also appears to be totally random.
Route 225. What the crap? I can't even remember where in the game this is. I can't determine the genre of the melody. Random autotuning? This game was just so forgettable.
Route 24. The adventure has started. Things aren't only easy. You have to do your own laundry, there isn't always a dry place to sleep, and you sometimes go all day without meeting anybody. It's a challenge, it has its ups and downs, but you don't regret anything. This is life in the field. You've become on good terms with your growing team, and your starter Pokémon has become a close friend already. You begin to get the hang of organizing your bag, and how to prepare the field rations efficiently. You're starting to realize what it is like being a trainer, and you like it so far.
Route 104. Here comes the king of the world! Just a few days into your adventure, and you're already overlooking the sea from the cliffs west of Petalburg. The weather is brilliant, the breeze plays with your hair, your Pokémon are happy, and your Pokémon have grown a lot stronger since you left Littleroot. You have even caught a couple more, and started to train them. The people you've met so far have been really nice. Man, training Pokémon is awesome! On to Rustboro!
Etc. The D/P music is, with a few exceptions, rather soulless. Most of the tunes don't convey a setting, or illustrate what's going on around you. Listening to it doesn't bring back any memories for me. The Route/town themes all become too boring, too generic.
That being said, Black/White does it mostly right, though. Had I been ten years younger, I would have been buzzing with nostalgia upon hearing its music already.
EDIT: I'd like to be proven wrong. Please try to hammer some sense of nostalgia into me. I might view this with the dark-tinted glasses of prejudice, perhaps Pokémon stopped being as magic for me some time during Gen. III, and that it didn't become nostalgic until recently. Perhaps D/P happened to be made during an unlucky period for me, those pesky early-teen years where the magic of childhood fades, but the nostalgia filter isn't put properly in place yet.