You can take a look here for reviews of various power meters. The article is a bit dated, but it should provide a good starting point. As for the other functions, you'll likely need a more traditional cyclocomputer in addition to the power meter. I personally use a CatEye Astrale 8 (probably the same model as Nermal's), which, as he mentioned, measures cadence in addition to the usual speed, time, distance, ... One nice thing about the CatEye is that it measures speed from the rear wheel instead of the front, so that you only have to route one wire down past the bottom bracket instead of a second wire down the fork to the front wheel.