Check out these knots
Zeppelin bend (loop also) - probably the best bend.
Alpine butterfly loop (bend also) - best knot for making a loop in the middle of the line
. The hand method is super easy. I like this as a loop over the bowline in some places because it dresses neatly.
Ashley stopper - as mentioned, the largest stopper for a given rope size.
Double overhand stopper/slip knot - clean looking stopper and a nice compact slip knot.
Adjustable grip hitch - great slide and grip hitch for making adjustable loops.
EDIT: While looking stuff up after this thread I also reminded myself of one more nice knot:
Surgeon's knot - a slight variation of the reef/square, one extra turn when you first tie it that makes it easier to tighten down and more secure.