I have a Nashbar branded wireless model (about $30) and a Cateye Astrale 8 (<$30). The Nashbar was my first computer and I like it a lot. It has just enough features and is very easy to set up and use. As a second computer for my other bike, I picked the Astrale 8. I wanted a computer that measured cadence. It works well, but lacks a couple of features I like that the Nashbar computer has, namely, a programmable odometer and a pace arrow.
Good luck with your choice,
desmobob