Make a list of all the characters in your icons. (Although you may have more than one icon of a single character, they only go on the list once.) Alphabetize it. Take the first two people on the list; that's your first pairing. Second two people; second pairing. etc.
(Turns out I don't have that many characters on my icons. I've got a few more real people - Alan Rickman, ASH - but I hate RPS, so naaaah for that. And I have many text icons.)
Calvin (Calvin & Hobbes)/ Captain Jack (Doctor Who) Oh, dear. Just a world of no. My brain is shrinking away from the thought.
Daniel Jackson (Stargate)/ Elton (Doctor Who, from Love & Monsters (he's dancing on the sofa in this icon. At least, from what I remember, it was him.) Huh. Well, I dunno. Slightly weird...they could investigate alien stuff together! More perfect than I thought at first.
Gregory House (House) / Ianto (Torchwood) Oh dear. This is a definite D/S relationship if I ever saw one. Actually, could be distinctly interesting.
Kaylee (Firefly)/ Lord Peter Wimsey (DL Sayers books) Guh. Interesting. But I really want to swap these ones round and get House/ Lord Peter (teh HAWT!) and Ianto/ Kaylee (teh CUTE!! Eeeee!)
Mr Finch (Doctor Who, played by ASH) / the Ninth Doctor Oooh, yes. I'd love to see this. Yum. And also INTENSE.
Rose (Doctor Who) / the Tenth Doctor Well, fair enough. It's Twoo Wuv, and I wouldn't want to wish either of them on anyone else.
V (V for Vendetta)/ Veronica Mars Hahahaha. The world is doomed. This is a brilliant pairing, and I want someone to write it.
Wash (Firefly) / Willy Wonka Uh. Heh. OK, funny. And weird.