The ultimate bike computer.
I got cheesed off with cycle computers generally a while ago, both wired and wireless varieties. I now use a small sat nav unit (garmin foretrex). It fixes securely to bike bars, gives accurate speeds without having to calibrate the wheel, and a whole host of other info of dubious value, but nonethless fun to browse. I use the same unit on my bike, my off road motorbike (I did a lot of adventure motorcycling in India), and cross country trekking (on foot). They cost a bit more (mine cost about £80), but a couple of brackets lets you easily clip it from bike to bike, and it comes with a wrist strap so you can actually wear it on your arm - so you only ever need one unit. The bike brackets are secure but quick release so you can slip it straight off the bike and into your pocket when parked up and the unit is fully waterproof. The batts. have about 8 hours life on a full charge, oh and you can illuminate the LCD display at night, so you can still see it then.
I didn't even bother to fit the freebie computer that came with my bike. Too much effort, for too little reward - and I don't like tying things down to my forks, very close to the spokes with zip ties!