I ran across this exercise a while back, and I do it every other leg workout with great results. It's like a cross between a lunge and a deadlift. I didn't make it up so it may have an "official" name, but I call it the single-legged deadlift.

Get a flat bench and stand perpendicular to it (center yourself to the bench) with your back facing it. Have a barbell set up in front of you too. Now, bring one of your legs back and rest your foot across the bench without hooking it over the other side. You'll probably have to hop around a bit until you get the perfect place for you front leg. I tend to get my front foot far enough out in front off me to get a good stretch on the glutes and hams at the bottom of the movement and to prevent lockout at the top of the movement. Next lean down in the same manner you would a deadlift and grab the barbell (I like to keep both hands in an overhand grip for this movement). Now push back up with the same form as a deadlift, but focus on driving more with your legs than pulling with your back. Continue on with as many reps as your choose to torture yourself with.
Since it has a tendcy to fry my nervous system, I rest about a minute between doing each leg, rather than going immediately from one to the other and then resting.

You can go down very deep on these without bringing your knee past your toes if that's a concern for you. It very easy to rely mainly on your glutes and hams to push up, so make sure to keep your quads tight and use it to drive up also. Obviously don't expect to be using alot of weight either, this is definately one where pride=injury. I've yet to use DB's yet, but I like that the barbell keeps the weight in front of me, retaining some of those deadlift characteristics.

I found that placement of this exercise is key. This is how I typically use it in a workout:
leg extensions - 2 warmup sets,
squats - 2 warmup sets and 4 or 5 working sets,
leg presses - 1 warmup set and 3 to 4 working sets,
single-legged deadlifts - 1 warmup w/bodyweight and 2
or 3 working sets
hack squats - 1 warmup set and 2 or 3 working sets
leg extensions - 2 drop sets
(I do ham specific execises with back later in the week)

Personally I feel this is the best spot for it; right after the mass builders. I did it after squats and before leg presses a couple of time, but it didn't seem as effective. It pumps so much blood into your legs, back, and core. It will fry your nervous system too if you're not careful.

Anyway, give it shot and see what ya think. Peace.