List of pixel art and spriting tools

[Khris]

Go to Edit -> Tools (or press "C"), then check "Onion skinning".

[Anian]

Go to Edit -> Tools (or press "C"), then check "Onion skinning".

Thank ye very much.  I guess it was just too obvious for me to see.

[RickJ]

I have been using the free version of Gale and find that it saves an incredible amount of time.  The free version is minus a couple of "webie" features but does not have any nag screens or other "free version" annoyances, so 
Abstauber you may want to update your original post to bnote there is a free version.

ASE sounds pretty good also, I'll have to give it a try.  Thanks for the info.