I've noticed that when I do crunches and other ab exercises, my hip flexors are doing the brunt of the work and not my abs. I try to keep my lower back flat against the floor, but that doesn't seem to be enough since I'm now feeling some pain in my groin/hip area. Any suggestions as to what I can do to make sure that my ab muscles are being targeted?

This is just a hunch (since I can't see your technique), but you may be straining your hip flexor muscles which are in fact doing the brunt of the work when you do a full sit up. What I mean by that is starting from the floor and raising your trunk all the way to a 90 degree angle. Beyond about 45 degrees, your hip flexors do the work, whereas your abs do the work at the beginning. So, the bottomline is to do crunches only to a 45 degree angle position. However, that does not mean you should never make your hip flexors work either! It just depends on what you are wanting at the time.

Thanks for the suggestion! I did some ab exercises last night and made a conscience effort to relax the hip flexor muscles as I was crunching up. I think I may have been going beyond the 45 degrees. :)