dailyicons (formerly "tv_icontest") - A 20in20 type of icon challenge.
You sign up with a claim (e.g. a Paring, an episode, a celebrity,...) and once prompts are posted your task is to make 20 icons in 20 days in accordance to your claim and the prompts!
Rule Overview/FAQ
Round 4 Sign Up
Round 2 Tie-Breaker Voting
Meanwhile, Round 3 icons are due on Monday at Midnight, but until then you can still join and make icons:
Round 3 Sign Up (open during the round)
Round 3 Prompts

icontest_needs - A place for discussions of mods, pimping icontests as well as asking for entries and/or votes. There's also going to be a masterlist.

fandom_caps - A place to share and request screencaps. Open to all fandoms!
Rules, FAQ,...

icon_help is a place to share tips about making icons, post tutorials and questions. You're also welcome to share resources such as screencaps, brushes and textures you like to use or made.

10prompts - Challenge community where you can pick a table (10 prompts) and write stories for. All fandoms as well as slash, het and gen are welcome. All questions can be asked in the rules post.