If you thought National Novel Writing Month (Nanowrimo) was a little too insane, Script Frenzy - the contest to write a 100 page script in a month might be up your alley. Instead of trying to write 50,000 words in a month, you try to write 100 pages of script - which is a lot less writing. I think the lower level of challenge has something to to with its lesser success (only around 6,000 people are participating in Script Frenzy, compared to 100,000 for Nanowrimo), but what it loses in sheer herculean challenge it makes up in variety. Participants are encouraged to write plays, movies, tv series, and comic books.
Personally, I'm going to branch out beyond those suggested targets. If all goes well, by this time next month I'll have written an adventure game.
I'm not certain since the site isn't active yet, but I think you'll be able to track my progress here.