I use a Harris ultralight HB25S, pretty tall for some people while laying prone, but works great for me in a kneeling or sitting position. I don't find myself shooting prone often, and when I do I use my pack as a rest, as its much more solid.
A swivel bipod is worth the extra money and weight, I can take or leave the notched leg models. I have some that are ok, but I prefer the non notched version.
