NOTE: This thread was originally started by Dylan, the previous mod. I've cleaned up the bad links, there currently shouldn't be a single non-functional link in the thread. Some of the original text belongs to Dylan, I'm going to leave it here but I'm merging my post with his to avoid confusion.
This is a topic to post good spritesheet sites. No ROMs. The Shyguy Kingdom Lots of random games here.
Sprites INC. How did I forget this? The ULTIMATE Megaman sprite site.
Sonic Fan Games HQ There's some Sonic stuff here.
Ragnarok Online: Battle for Sprites Has some hats and monsters, mainly.
Nes Snes Sprites General NES and SNES sprite resources
The Spriters Resource | Main Page A wide variety of sprites based on many platforms.
(5/26/11
EDIT:
Dead links removed, others updated to current addresses - A.I.)