You can get the Gimp if you don't want to spend any money, but as far as I'm concerned the interface is such that it's more trouble than it's worth.
There are a lot of decent, cheap and user-friendly image editing programs out there -- Ulead Photoimpact is a preference of mine in the sub-$100 set (I think it's under $100). Paint Shop Pro is good too. If you're looking for a really solid program, Photoshop Elements is affordable and it does all the most-important stuff Photoshop does. If prices are more or less the same between the other titles I've mentioned, I'd probably go for Elements.
I don't know... I haven't been in the market for a while...
EDIT: I also think stuff like PictureIt and Photoshop Album do a lot of the really rudimentary stuff... and probably Picasa, which is a free download from google (
www.picasa.com)