I just got a Samsung YP-U1Z (1GB) and I love the thing already. It is very small, and has an integrated USB jack so you don't have to fuck with cables or anything like that. It is about the size of an iPod Shuffle, but is not the same size so you can't use the accessories for it. I got mine as a present, but I have seen them for between $100 and $125, depending where you look.
The Sonys were nice, but more expensive. They have an insane battery life, like 50 hours or something like that. My Samsung only has a 13 hour battery life and takes about 2.5 hours to charge. I wanted a Samsung because the issue with many Sony products is DRM shit, or not being able to play some types of music files because they aren't copy-protected. Be sure to investigate that with Sony products before you purchase them.