I just got a Cateye CD300DW wireless speed and cadence data for $99 new on eBay.
http://www.cateye.com/en/products/vi...d=6&subCatId=0

I've only used it for the last 3 days, but I liking it very much. Nice and big easy to see numbers. It lights up. Awesome mount, but I still had to buy a computer mount for my Aerobars.

I have a trainer that came with a DVD that instructs you to use a specific variations of cadence during the workout. I got an awesome workout on it yesterday keeping up with the proper cadence of the workout.

But I'd also check out the Vetta listed above. A heartrate monitor would really be nice too. For me, I use a HR monitor already that downloads to my Mac, so I'm not really interested in that feature.

Here's some eBay listings that I find is $50 less than retail:
http://search.ebay.com/CD300DW_W0QQfromZR40QQsojsZ1