For hard floors, I have been really impressed by my Makita cordless vac. It's awesome. For carpet, there is nothing better than a plug-in Miele, there is no good cordless vac for carpet, don't even try.

EDIT: I have 2 Siberian Huskies, so I know what I'm talking about here :)

I forgot to mention Festool shop vacs. Not cordless, but excellent machines.