Don't expect to stave off dehydration by drinking urine. Your body expels salts (and other substances) through urine. Thus you'll die from hypernatremia drinking urine or seawater, just as happens if you don't drink water at all.

Apparently blood and alcohol are also bad. They are processed as food, which requires large amounts of water from your body. Thus while they're both fluids, they result in a net loss of water.

Fish apparently have a column of fresh water near their spine. You can cut them open and drink from this. You can also suck fresh water from their eyes.

Edit: Oh, hey, a citation:

http://en.wikipedia.org/wiki/Urophagia#Attempting_survival

Everything else is from "Complete Survival Manual," Michael Sweeney.