Hetalia is the only one I actually contribute to
Most of the other fandoms I'm in I play more of a passive role or as anon mentioned I don't actively seek out fan contributions

Star Trek (TOS and Reboot)
Sailor Moon
Sherlock
The Hobbit
The Avengers (movie verse more than the comic verse)
LA Noire (nothing going on in it)
Sweet Fuse (same as above)
Saint Young Men