The Schwinn cyclocomputer at wal-mart cost me $10 and lasted 1,600ish miles before I broke it. Good bang for the buck. If you're looking for something a little nicer, I'd suggest the planet bike protege 9.0. It's pretty basic, but has some nice features such as a 2nd wheel size odometer and a temperature indicator. The temp indicator was the deal breaker for me (I'm a weather dork, heh). Costs around $25 when it's on sale.

I don't have clipless pedals/shoes yet, but I wouldn't buy shoes online without trying them on first. If you have a Performance bike near you go there. You'll be able to find a lot of the stuff you want/need for a pretty good price or check at the local bike shops. If you're not sure about the quality of a product post a question about it on the forums or use the search function. I've learned a lot about products searching the forums.