Figured I'd contribute some knowledge.
: The mighty beasts of thunder, Electric-types!
-Easily covered weaknesses
-Many Electric-types have good coverage options
-Electric Pokemon will save you in the war! They'll zap your enemies into paralysis!
-Absolutely no entry hazards. This means that your opponents are never punished for switching, which gives them an advantage
-Most viable Electric-types are specially oriented, meaning that many Pokemon will simply overlap
-Simply not much variety: very few Electric-types have neat secondary types or abilities that make them special
-Zapdos is notable for it's immense offensive potential, as well as solid defensive potential, and most importantly, an immunity to Ground-type moves, a type that ravages most Electric-types. SubRoost with Toxic and Pressure to stall is a great thing to have. Zapdos should be on every mono-Electric team, no exceptions
-Jolteon, Manectric, and Raikou are all speedy, powerful Special attackers, each having something special that separates them from the other two. Jolteon has it's insane 130 base speed, Manectric has Lightningrod and access to Flamethrower/Overheat, and Raikou makes for a great Calm Mind sweeper, as well as having access to a nice Fighting-type move in Aura Sphere.
-Rotom-W, Rotom-C, and Rotom-H are unique forms of Rotom that have nifty secondary types. Rotom-W's unique Hydro Pump is very useful in handling Ground-types, as is Rotom-C's Leaf Storm. Rotom-H's Overheat is somewhat less noticable, but any team likes having a strong Fire-type move, and if you don't run Heat Wave on Zapdos, it's a good alternative. All 3 formes are capable of spreading burns with Will-o-Wisp, making them effective at neutering physical threats.
-Electivire and Luxray are notable for having good physical stats and movepools, something a mono-Electric team craves desperately. Both have Wild Charge as a physical STAB, decent coverage in moves such as Cross Chop, Superpower, Ice Punch, Fire Punch, Earthquake, and Crunch. Either of the pair should be on any mono-Electric team
-Magnezone is quite useful, as it's a mono-Electric team's only answer to powerful Dragon-type attacks, as well as being capable of ending mono-Steel teams almost single-handedly. A SubCharge set is it's most viable option
Lanturn, Eelektross, Galvantula, Electrode
These Pokemon have much less to offer than others, but are still notable. Lanturn's Water-type STAB moves, as well as access to Heal Bell, can prove useful, but on the whole, it's not as good as Rotom-W. Eelektross is rather underwhelming, but immunity to Ground, as well as no weaknesses, could be handy. Galvantula is rather weak compared to many other Electric-types, but a Bug-type STAB and Thunder that is usable outside of Rain are calling cards for it. Finally, Electrode can be used as a suicide lead, to set up Rain and then blow up, allowing for it's teammates to go crazy spamming Thunder
Immune to Ground: Rotom-A, Zapdos, Eelektross
Neutral to Ground: Galvantula
Honorable mention: Air Balloon is very useful to get free switches for Pokemon weak to Ground, which is very helpful, considering Ground-type moves are useful overall