[Stumpkiller]

Let me start off the category with two knots that I feel are the best for their respective uses. 

For small flies to tippet I can't think of a better knot than the Orvis Knot.  It's a figure-of-eight knot with an added final tuck.  Easy to tie, though not quite as easy as the Davy [Wotton] Knot - but somewhat stronger.  Though when the light is failing the Davy Knot is a good choice because it is so simple. 

The other is the [Lefty] Kreh Loop (aka Open Clinch Knot and Anti-Slip Mono Loop).  I use this one for streamers where I want some action.  Also great anyplace you would use a Rapala Knot.  Not quite as strong as the Rapala but easier to tie and the tag-end faces the fly so it is slightly more weedless.

Here is the Orvis Knot tutorial that includes both of the above.

http://www.orvis.com/orvis_assets/files/index.html

[HARL]

    Will have to give them a try .

[woodchucker]

I kinda like that Orvis knot!!! I'll have to give it a try! Usually I use a clinch knot, (without the "improved" lol) Or a uni-knot!
The uni-knot is easier to tie, with these old eyes, and fumble fingers, but it eats up a lot of tippet!