Star Wars (easy) = Darth Vader - Guessed by Solez (see SW Top 10)
Marvel Comics (note comics, not movies) = Spider-man - Guessed by Judy He's the most relatable hero, who's story is a real coming of age tale. He's also had some genuinely funny banter (In the comics at least)
Death Note = L - Guessed by Judy I just love his quirky nature and his unbridled weirdness. I was kind of annoyed at *SPOILERS* his rather unceremonious death, but he's still a great character
Trigun (Animé) = Vash the Stampede - Guessed by Judy Similar to L, or Jack Sparrow he acts like a total spazz but is really a kickass warrior, oh and did I mention he's a pacifist
Heroes = Sylar - The main villain on the show, his possession of the coolest power (telekinesis) and his menacing nature (except in some parts of volume 3) make him my favourite character
Resident Evil (Games) = Leon S Kennedy - Guessed by Judy (see top 20 games characters)
Metal Gear Solid = Solid Snake - Guessed by Judy (see top 20 games characters)
DC Comics (again see Marvel) = The Batman - Guessed by Solez Easily the best DC hero, noone else even comes close
Family Guy = Peter Griffin - Guessed by Solez Close between him and Stewie but Peter's had less character decay so he wins. Plus he's just so hilariously dumb.
The Simpsons = Mr. Burns - Sideshow Bob being close, Mr. Burns is one of the few characters who's still as funny as ever
Kirby = Meta Knight - Guessed by Judy (see top 20 games characters)
Star Fox = Wolf O' Donnell - Guessed by Judy (see top 20 games characters)
Transformers = Optimus Prime (though Dinobot is a close second) - Guessed by Judy He's just awesome incarnate, shoved into a robot. The famous Peter Cullen voice has nobility, power, and heart all in the same line, plus he looks great in a fight.
Lord of the Rings = Gandalf The Grey/White - Guessed by Solez Perhaps it's Ian McKellen's portrayal, but I really think he has a great mixture of kindness and strength, something the movie Dumbledore lacked.
Pirates of the Caribbean Trilogy = Captain Jack Sparrow - Guessed by Judy Anyone who knows me knows this. He's my favourite movie character of all time full stop.
The Matrix Trilogy = Smith - He's a massiva asshole, but he does it wit such style you can't help but respect him, Morpheus is a close second.
Friends = Chandler - Guessed by Judy Though I like all the Friends similarly
Yu-Gi-Oh! The Abridged Series = Seto Kaiba or Kemo, Kaiba's just a big jerk, but he's hilarious.
Pokémon (Games) (in this case character includes creature) = Blastoise - (see top 20 games characters)
Genshiken (Animé) = Kousaka - Guessed by Judy I just love his total obliviousness to anything, coutnering any situation with ^_^. In fact my favourite scene in "Genshiken" is when somethign shocking's just happened and the angle cuts in turn to everyone on the table who's wearing a horrified expression and Kousaka's still going ^_^