I recommend the http://www.rest-timer.com Great for making the workout more interesting and helps to reinvigorate you. Good stuff. and cheap too.

How about doing your leg exercises in 3 sets of 7 each side, alternating between the legs with no rest, first set concentrate on strength, 2nd go for speed, and 3rd for explosiveness with a little hop? Keeping the rest between sets and exercises as short as possible will really challenge your endurance...