I have a vanguard that telescopes to the point I can almost shoot it standing up. I've shot off of it kneeling plenty of times. It also comes w/ 2 dove tail mounts from which the bipod quick detatches. Its light and inexpensive, i think I saw it on camofire for $65.. I also have the smaller bipod for shooting prone.
The vanguard has a spring to allow movment left right forward and back... due to this I wouldn't recomend it for a heavy rifle.