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.
I have the Cateye Astrale 8 mentioned above, plus 2 Cateye Enduro 8's on other bikes. The differences between the Astrale and Enduro are:
The Astrale has a cadence sensor
The Enduro has slightly heavier wiring, two trip gauges, pace arrow, and is slightly cheaper than the Astrale.
I bought the Astrale first, but then found that I really didn't use the cadence feature, so I switched to the Enduro because of price (I really don't need 2 trip gauges, though the pace arrow is growing on me). I've used both of them in heavy rain and have had no problems. Setup is the same on both, and the displays are large on both. I can recommend both.