The annual Halloween fanfic gift exchange, trickortreatex, is currently in nominations (ending on the 8th).

This is a low-key exchange with a 300-word minimum. There is a new mod this year who is allowing people to nominate up to 10 fandoms with up to 10 characters and/or pairings in each. Nominate here.

Lots of fun! I've done it for several years now.