Let's hear 'em. I currently do 125 situps a few times a week, and I want to expand my routine. I want to get a serious six pack.
The Ab-Wheel! I made mine but they are inexpensive at the store.
the flag
i really like swiss ball crunches.
or for MMA/BJJ try doing your crunches on your back and then place the ball between your knees (like you have the ball in your open guard) and as you do the crunches...bring the ball close to your upper body...works great and functional!
L-sit or seat... Real core challenge. Sit ups and crunches are pretty gay for the most part. I only say that because people think they are the end all exercise for the core, the plank too. Challenge your core and get creative.
http://www.beastskills.com/L%20Seat.htm
Hanging Leg Raises, the various stuff on beastskills and crawling on a Powerwheel are my favorites.
single handed ab wheels so you can get a more varying range of motion
Anything that you see in gymnastics or OL!
Legraise, V sits, hollow rocks, front levers, planches, OH squats, L-sits, Knees to elbows, power snatches, C & J, Dragon flags.
Baz
hang your legs over a pull up bar so you are hanging upside down. keep your hands tight to your chest with your arms crossed and touch your elbows to your knees
hopefully will be able to get out of bed in the morning
i like using a slant board w/ a weight behind my head going to parallel and holding for 5 seconds at bottom.
Lots of great suggestions already.
Breath integration is fundamental to effective core training. I teach many of my clients the integrated core exercises from "Be Breathed", a video available from RMAX. There's a link on my site, www.CSTMinnesota.com
If you can do 10 Butterflies (from "Be Breathed") slowly with good control, then 100 crunches will be easy.
Prasara Yoga also includes a boatload of great exercises for developing abdominal strength, endurance, and control.
Jason Erickson
www.CSTMinnesota.com
Front squat, woodchops with a cablecrossmachine, ab-wheel, weighted crunches...