Really getting into this whole Tri thing -- NTP rocks! I love technology so I want to get a bike computer. But what features are useful? All have distance/speed, but what about cadence and/or heart rate? The spinner at the gym has those -- is that useful on a road bike? Are there other metrics I should be looking for? Also, is wireless the way to go? So much to know! Any advice welcome!
I originally got a simple Cateye wireless that showed the basics of distance and speed but recently purchased another that included cadence which I find very helpful. Check out the reviews online between brands.
The only issue I've had with wireless is sometimes there is interference on the trainer from other signals in my apartment but if you are not riding on the trainer then I'd suggest wireless.
Hope that helps!
Don't overlook something like a Garmin 305. You'd have data from swimming, biking and running. Cost might be a little more than a bike computer from your LBS, but a Garmin 305 with a cadence sensor through Amazon was pretty reasonable.
Just to start with, I'd probably second Ryan's recommendation of the Cateye Strada Wireless. Easy to install and has speed/distance/time. All you really need to start.
Cadence is nice to have, but once you really confirm that your cadence is where you want it to be (~90rpm), it's only used occasionally because you develop a good feel for what 90rpm is.
Heart rate is useful if you want to....do heart rate training. Some people like doing that, some don't. Personally I don't so I haven't bothered with it.
If you really want to future-proof your bike purchase and have the funds available, a Garmin is a good one to go for. If you want a multi-purpose watch I'd probably suggest the 310XT, not the 305. And the Edge 500 is great for a stand alone bike computer. The great thing is that these are ANT+ compatible. ANT+ is an open source wireless data transfer method that a lot of the manufacturers use. You can add an ANT+ speed/cadence sensor, ANT+ heart rate strap, or use an ANT+ power meter (powertap, quarq). The thing is that the Forerunner 305 uses ANT+, but cannot show ANT+ power data, while the 310XT does. Again, you probably don't have a power meter or know if you will ever want one, but it's a nice feature to have just in case.