I'm having trouble narrowing down my list of offerings AND my list of requests, though.
I started off by going down the Yuletide 2012 Tag Set and eliminating everything that I've never heard of. Then I eliminated all the fandoms that I'm completely uninterested in. Then I eliminated all the fandoms that I wouldn't read fic for. Then I eliminated all the fandoms that I wouldn't write fic for. That left this list.
Anime & Manga
Pet Shop of Horrors
Yami no Matsuei
I'm not a huge fan of these genres anymore, but Initial D is one of the only anime series that I've watched more than twice. Pet Shop of Horrors has one of those plots that I adore and it has so much potential to write about. And Yami no Matsuei is so bound up in tropes that I love that I can't resist it. I'm... not sure that I could write for Initial D, though, so I should perhaps strike that from the list.
Books & Literature
Raffles by E. W. Hornung
Valdemar Series by Mercedes Lackey
Actually, while I love both these series (and a LOT of the other books I cut off my final list), I'm not sure I could write in them. Well, I could totally write Valdemar, but only original characters, not the requested characters, lol. And I can't fake being a 19th century author well enough to do Raffles justice. I would TOTALLY love a Raffles story written for me, though. Bunny is the bee's knees!
Cartoons & Comics & Graphic Novels
Cable and Deadpool
Incredible Hulk (SHE-HULK/Jennifer Walters, Leonard Samson)
DEADPOOL AND SHE-HULK!!!!! Yeah, Deadpool is on this particular section of my list thrice (he's included in X-Force, too) because I love him so much. I'm totally going to request a Deadpool story. Problem is, what era? Do I want original appearances and his interactions with the old X-Force team (ala, Cannonball, Boomer, Siryn, Cable, Domino, Shatterstar, and Rictor)? Do I want the first Deadpool series, featuring such characters as Weasel and Blind Al (a particular fav)? Or do I want the extra special OTP that is Cable/Deadpool? I CAN'T DECIDE! I NEED LITTLE YELLOW BOXES TO TELL ME WHAT TO DO!!! Also, She-Hulk, bestest hero in the Marvel U. Yeah, that's happening. I'm pretty sure that I'd love to write PS 238 fic, too. I mean, who doesn't love writing about a school for superheroes? Plus, I got all the newest trades at Comic-Con, so yeah.
BUT WHAT HAPPENS NEXT!?! I want to knoooooow~! For ALL the characters in this movie. And I also think I could totally write a story about it, too, because whenever I watch this movie I daydream about what happens next.
Absolut Vodka Greyhound Commercial
This is only the best commercial in the history of ever. I would write the fuck out of this. I'm actually less interested in reading something someone else wrote for it, but it might be fun, too. I would, of course, if I wrote something for this commercial, need to listen to lots and lots of Swedish House Mafia while writing it. :D
Yeah. Alien Nation... I totally have fic in my head for that. Babylon 5 is love. Bernard from Black Books would be hard to write, but I could totally do a Manny POV or a background on Fran piece. Brimstone is amazing and I <3 Zeke Stone and his evil tattoos (crossover with Reaper, yes please!). I want to write and request Elementary -- I've been saving up a lot of "mystery" ideas I could use to write it, but this fandom is so fresh I don't know if I should play in that playground yet. I've already written Incredible Hulk fanfic, but I recently tried to go back and re-watch it since Netflix has it all and I couldn't get through the first episode, so maybe not. I have been mainlining Lewis fandom lately, so I could totally request it, but I don't think I could write it. Quantum Leap would be interesting, and I LOVE time travel stories. I'm watching episodes of Reaper right now and I think I could write it, but I'm not sure I care about the show enough to actually read fanfic about it, so maybe not. seaQuest... I had epic fanfic in my head for this show once upon a time, but that time may have passed. I'm not up-to-date on Warehouse 13, either, so maybe not.
I'd totally write Glitch fanfic... except that the requested characters are Gwendolyn, Esquibeth of Inari, and the Rube. Bleh, I'd want to write about the Giants.
OK, so what does that culling reduce my list to?
Pet Shop of Horrors (request and offer)
Yami no Matsuei (request and offer)
Cable and Deadpool (request and offer)
Incredible Hulk (request and offer, Jen Walters char only)
PS 238 (request and offer)
Love Actually (request and offer)
Absolut Vodka Greyhound Commercial (request and offer)
Alien Nation (offer)
Babylon 5 (offer)*
Elementary (request and offer)*
Quantum Leap (offer)*
Anything with a * is something I'm waffling on, for various reasons.
My list is still too long... ;_;
Well, writing all that down helped a little bit, anyway, I guess.