Here is the best one I've seen, the individual discharge tray with LEDs is the best because it shows you when all cells are discharged without using a DVM.
Look here: http://www.schumacher.clara.net/equaliser.htm
for the tray type discharger circut.
Look here: http://www.schumacher.clara.net/leddisplay.htm
for the tray type discharger with LED indicator circut.
You must use a some type of pack discharger first to get the pack close to being discharged first as the tray discharger will take a LONG time to discharge your whole pack. Use a bulb type discharger like a Deans or an Integy 20A or 30A discharger to discharge the pack, then equalize the individual cells in the modified tray using the LED version of the circut. This makes for very strong running packs but only use this tray for NiCad batteries, NiMh batteries don't like the trays!