Doug, here is yet another list:
1. Bowline with "Yosemite Finish" backup
2. Clove Hitch with backup- typically a Double Overhand stopper knot
3. Figure 8 Bend, backed up with a Double Overhand knot at each end
4. Butterfly Knot, a multi-directional loop knot, very useful for tensioning a line

I almost always backup the knots from habit and previous training, and it's a good way to keep the practice-- so I guess that the Double Overhand used as a backup knot brings this list up to five knots..... but I couldn't part with any of them, so five it is.

Tim H., Edmonds, WA