I have a Cateye Double Wireless computer:
http://www.cateye.com/en/product_detail/251
with wireless speed & cadence. It has one sensor for both speed & cadence, mounted on your chainstay. Speed magnet is rear wheel mounted.
I love this computer. All the information you want (current speed, current cadence, ride/lap time and distance) on one screen, without having to switch views, and for me at least, it's been super reliable.
Unlike the annoying Vetta I have that routinely blinks out on me during rides.
I paid $180 last year at LBS, but my boyfriend recently scored the same computer for $100 at Nashbar (computer sale + "one day only" 20% off all orders).