The Knot Link... Who knows might need it someday...

[Metal Twister]

http://www.animatedknots.com/knotlist.php?LogoImage=LogoGrog.jpg&Website=www.animatedknots.com

[jgorm]

That is a nice list, but IMHO there are only a couple knots you really need to know.  In order of usefulness.
1. bowline: for tying stuff off, making loops, etc.  Easy to untie after insane loads.  By far the best knot!!! If you only know 1 knot it should be the bowline.
2. fishermans and double fishermans:  Great for stuff that you want to cinch tight.  Super hard to untie after loading.
3. figure 8 (including follow through and double style): climbing tie in and stopping ropes from going thru stuff.
4. clove hitch: great for pulling stuff up off a biner, log, pole, etc. Semi locking so it resists going back down / out.
5.  Prusik: For when you need to ascend a fixed rope, or hold another rope tight when you can't tie a loop in it.   
6. square knot:  I still sometimes use it to tie to ropes together, but only if i need them for a non heavy load temp thing.  otherwise i'll tie a bowline to a bowline so i can untie them in a second.

[84sr5]

This is a great link, every one needs to have one or two knot tying skills its just a good ability to have.

[SNOTROCKET]

i can pretty much make a mess of a knot and it usually holds.