They are all rated for 3W, but you can actually get a lot more out of them by wiring LEDs in series.

Another plus for dynohubs is that if you're capable, they provide lots of opportunity for tinkering. You can make a light with an integrated battery (or large capacitor) for standing lights. I'm in the process of incorporating a charging circuit for an extra battery for a helmet lamp. You can even rig them up to power electronics (with care).

All of this, however, is more costly than just buying a rechargeable battery, but it's fun.