I've used Ubuntu and find it good. If you go to www.ubuntu.com and follow the links, you should be able to request free CD packs. I got five packs and distributed them around my (geek) mates.
The pack contains a 'live' Cd and an install CD. You can boot Ubuntu from the live CD without making any changes to your system and see if you like it (much like booting off floppy disk). If you like it, go ahead and install it.
It's a good idea to partition your target disk drive beforehand so you can put stuff where you want it during the install process.
Graham Stewart, July 2006