I pretty much use 3 knots when Im fishing. Its all I really knew for years. The uni is the old fishermens knot that will work for many many things. The palomar is obviously the easiest and the best for braided lines. Both of these you can tie in the dark.
The palomar is also what I used for tying lures to the line with. Braid and mono. (Harder in the dark :) ) The rapala knot is a much better one to use when tying on lures though.
The only other one I knew was the snell. The rest were modified or shock leader type knots. Like double unis.