Zeldman gives a link to Photoshop 7 Keyboard shortcuts for Windows. On the Mac, substitute COMMAND (the Apple key) for CTRL and OPTION for ALT.
I'd probably know a lot more of these if I was still continuing my quest for a Photoshop Certification. I still want to get it, but the Java/Struts/XDoclet realm is more inspiring and more fun right now. I haven't touched the Photoshop 7 Bible in about a month! Maybe I'll get back into it, but I probably won't finish it this year.