The Art Corner - An artist community with useful services. Most of the site is on hiatus right now, but you can still visit their lively oekaki board and message board.
Monthly Anime Gaijin - Draw other people's characters! If you win, you get to have other people draw your characters next month.
Monthly Original Bishoujo - Same concept as MAG, except the characters must be pretty girls.
AnimeNation - An anime superstore. The real reason I'm linking it, though, is that they host art contests with nifty prizes.
Dream-Grafix - Get your artworks hosted, and participate in their contests.
GFXartist - Post your art, receive constructive critiques, and admire the works of the Elites... or become one yourself! This is NOT a place to look for "OMG KAWAIIIIIIIII!!!!111" type of comments.
Elfwood - A gigantic place for fantasy and sci-fi artists to share their works.
Music:
OverClocked ReMix - Myriads of video game arrangements by fans.
Darkesword's Page of Stuff - This guy does some really sweet musics! The server is kinda slow, though.
Destiny-Hikari - Lots of good vocal music make me one happy Keiiii.
Edgen - Good music with a cinematic feel (which is not surprising since he does compose music for movies).
Mostly Ghostly - Very distinctive stuff here. I likey! Most of the compositions are orchestra-ic.
Phai-Rock (Japanese) - Live violin is good stuff. Mmm... yes.
MUSIC na Kibun (Japanese) - Interesting remixes and original tracks. I love his piano tracks, especially Star Piano and the four seasons series.
In the Blue (Japanese) - Very nice ethnic and orchestra stuff, both video game remixes and original music. She also has a sweet singing voice, especially in Japanese.
Unknown Library (Japanese) - Awesome stuff here. Mostly mellow. I wish they'd post more ;_;