Personally, I like my Topeak Comp 140. It didn't cost very much, but it has cadence, which I really like. I'm trying to improve my cadence, so I keep that displayed. It also does speed, distance, average speed, average cadence, etc.
I really like going down a hill and glancing to the speedo to see it tracking at 29 or 30 MPH
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The only thing it lacks, IMHO, is a backlight. However, I wear a helmet light, so I just shine that on the display when I want to check things after dark.
I've had it on my bars for over 1.5 years and haven't had a problem. Rain, shine, snow, ice, whatever. My bike lives outside, and I don't take the 'puter off when I go in. Tough little device.