Whee! The Summer/Winter Holidays fest at wintercompanion is open and looking for sign-ups until the 28th of May! So if you're interested in writing some Doctor/Jack fic based on prompts or creating Doctor/Jack art, head over there! I signed up right away - heck, finding that community is probably the reason I ended up back on LJ in the first place, so sure as hell I'm participating. Maybe it'll make me successfully finish a story again!
And even if you don't want to participate, in July the fic and art will be posted in the community, so keep an eye on it! They've got both LiveJournal and Dreamwidth versions now, so neither site needs to miss out.
Another fest I'm planning to participate in is torchwood_fest, which is nicely low-pressure and has a lot of prompts. I'd love to finally write a whole Torchwood fic after starting many that aren't finished.