Picasa is an amazing program for sorting and doing basic edits to photos. I'm a photographer by profession, and I use Photoshop and all that jazz, but when I'm sorting and quickly going through several hundred photos, none does the job as fast, smoothly, and as well as Picasa. I've used ACDSee, Photo Mechanic, and other professional programs, but for my purposes, Picasa is easier and faster to use.
If you want to get into some slightly more serious editing work (because Picasa is meant more as an organizational tool than an in-depth photo manipulating program), Photoshop Elements gives you pretty much all the tools you're ever going to need.
I've also heard goods about the open source
GIMP. I've never used it, so I can't vouch for it, but give it a go on your system and see what you think of it.