Graphic Converter is an excellent program. It is worth the shareware fee, but you can try it for free (forever, actually, if you are cheap and don't mind some inconvenience).
Image Tricks is an Photoshop Elements type program. Free when I got it, but inexpensive now.
If you really want Photoshop then get Photoshop. You might want to wait for the universal version, though. There is iPhoto, of course, and various Paint and Draw programs like: Art Rage, Intaglio, Lineform, Pixen, Rita, WouldjaDraw and Zeus Draw. There is a bunch of Mac stuff out there, depending on what you want.