The Hugo awards seem to be the most prestigious awards in the SF world. They're also the oldest (first given in 195x).
The award is named after Hugo Gernsback, who probably created genre SF through his magazines (including Amazing Stories, the first SF monthly). He also created fandom -- his magazines, when they published a letter from a reader, also published the reader's address. This let the early fans of SF start corresponding and finding each other.
The Hugo awards are nominated and voted by the members of the World Science Fiction Convention; generally well-read SF fans. While no award scheme is perfect, I find the Hugos reward books I like more reliably than the others. Since these pages are about my personal relationships with books, that's all I'm interested in claiming.
As with any award scheme, the nominees are all pretty interesting. Claiming that any award comes close to honoring the "best" book (even of some restricted kind) each year is ridiculous, but most of the best SF does indeed get nominated for the Hugos and the Nebulas.
Laurie Mann runs AwardWeb.
The ISFDB can produce lists of awards from its database.