If you're looking for more junk to hang off your handlebars, the Adventure Cycling catalog has a simple bubble level that displays grade in real time. It's bound to be way more accurate than any of the electronic gizmos, whether they use a barometric pressure altimeter or simply rely on GPS data. They're notoriously inaccurate on altitude, although once you import the data into your computer, some of the software will correct the altitude readings against known points on your route.

I have to say, the new Edge models are very tempting. It would be really cool to have access to road maps like we do on the motorized-vehicle GPS units.