In Reply To:
[reply]There's a free option, too.
There are some incredible isometric hip flexor exercises you can do on your own. I don't know of a link offhand, but there's a lot you can do with some free floorspace and just yourself.[/reply]
Yup, just do several situp/crunch/leg lift/leg extension sets while watching TV one night. I typically end up doing about 1000 total reps split between ~250 situps, ~500 crunches and ~100 prone leg lifts/~100 standing leg lifts. The ones that really do a lot for your hip flexors is the standing leg lift...just stand there and lift your knee to the front. If your hip flexors are in really bad shape you'll be dying at sets of 25 for each leg.
If you insist on working the hip flexors, may I suggest doing situps such that you also do the horizontal version of the leg lift: 10 each leg without letting your leg touch the floor, switch to other leg, repeat. Shin stays parallel to the ground as you bring your knee to your chest when you sit up. I used to do this as part of triple jump training, where you actually use your hip flexor to raise your knee.
I'd also point out that isometric exercises are great for training your muscle to hold that single position; I gather that it doesn't carry over to the range of motion the muscle is suited for. Again, specificity.
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"Go yell at an M&M"