Our oldest daughter has a Disney Mix Stick. Its okay for her, she got it when she was 3 years old andjust recently started using it alot. The only thing I dont like is that you cant see what song is playing, you just have to keep clicking through until you find the song you want. I only paid $8 for it, so it works for what she "needs" it for.
Since she started using hers again, our youngest daughter started wanting something to listen to music on too, so she is using DH's old Sansa C250. It has a small screen on it where you can see what song it is, and a menu where you can search by artist or song. I think it cost around $25-30 on Overstock.com when I bought it for him for Christmas in 2009.