Hard ab workout!

or this one: (get it here, comes with instructional dvd. you will hurt. a lot.)

there's a Power Wheel 100 yd Challenge, and a video of some of the stronger athletes doing it here:

http://www.monkeybargym.com/power-wheel-100-yard-club-challenge.html

I worked out there for awhile, did their 60 Day Challenge- it was AMAZINg, I got a lot stronger, and more surprisingly, I got a lot more efficient using what strength I had, more balanced, used muscle groups better. Then I got pregnant. Just had my baby. Time to start all over again!

I think Jon Hinds is an incredible person/motivator, etc. 

Search MBG on youtube, and you can see him doing all kinds of cool stuff.

i do a new routine every 6 weeks, just for a bit of variety, mental and physical.

one routine: http://www.t-nation.com/readArticle.do?id=459670 , though i use an ab wheel not a swiss ball for exercise one. Do these 3 times per week. These are TOUGH. I use 5kg for the decline russian twists, and 7kg for the cyclone and the crunches. I am LOVING this 6 week phase!

another: bicycle crunches - as many as possible to failure, followed immediately by planks and side planks. That's one set. do 3-5 sets, and try not to drop off the numbers done and times on planks. Do these every day.

another: grab a weight plate, hold it against chest, bicycle crunches (aim to fail at 30). wait 30seconds, go again, wait 30 seconds go again. That's 1 set. Do 3 sets (resting 2-3 mins or something between sets). Do these every second day.

another: swiss ball leg raises (http://www.youtube.com/watch?v=qEUou_iKgF4&feature=related - use a mirror/window to make sure you're thighs are ALWAYS parallel to the wall, if you flex them inwards to you a bit, you're cheating yourself). Go to failure for 3-5 sets.  Swiss ball crunches (do these slowwwly, concentrate on flexing abs the whole way, and go back far enough so that you're almost about to fall off). Swiss ball oblique crunches. Regular crunches with legs raised, as in, lay down on the floor, thighs perpendicular to floor, shins parallel to floor, grab ear lobs lightly with thumb-finger, and crunch up to touch elbows to quads, and concentrate on NOT moving those legs. I usually do a couple sets of all of them, to failure, every day. In fact, check out the other videos by that guy.

another: http://www.t-nation.com/readArticle.do?id=459658 , i haven't done these yet, but they're my next-to-do.

There's more than one way to skin a cat, but those personally have worked verrrry well for me. Good luck!!