Today is Hugo nomination deadline
Run, don't walk, to http://www.denvention.org/hugos/08hugonomballot.php
What more's to be said? Hugo nomination season was brief this year; it's highly likely as a result that you wield disproportionate power if you nominate and vote because nomination numbers are always very low. Literally, every single nomination counts for this award, and books can get on the ballot with as few as 30 nominations.
Nomination for this award is perhaps the most concretely effective thing you can do to support the career of writers you like. Of course I'm shamelessly cadging for Queen of Candesce here, but there's plenty of other award categories that would benefit from your opinion, such as best short story, best novella, dramatic screenplay etc.
That said, if you're not already a member of Denvention, you're out of luck. I suspect this sort of draconian membership is part of the reason the nomination numbers are so low (doubtless there's a flame-ridden discussion thread about that around somewhere)--but hundreds of people who could nominate don't, and I'm sure many of them intend to but are caught with their pants down when the deadline passes.