Almost any Harris-style bipod will hook onto the front sling swivel stud. I've used Caldwell and BLACKHAWK! bipods with some success. As long as the bipod isn't meant to attach to Picatinny rail, chances are good it will attach to the sling swivel stud. Avoid barrel clamp bipods if you value accuracy. Chances are good they'll be more of a hindrance than anything.

Features I find useful are pivoting, which helps keep the rifle upright; a lever handle that locks the pivot in place, which is much easier to use than the little knob on some bipods; and notched legs, which are quicker to adjust when in position behind the rifle.