WHAT'S EVERYONE'S...

[Alhambra]

Ball exchange is definitely one of my favorites. I also like balancing in a pike position (I can't remember which workout Cathe has this in it...but I used to have to do it all the time as a teenager when I did diving so it's an old favorite and a definite ab burner).
The other one I like is the plank where you lift one leg, move it out to the side, then repeat with the other leg...I really have to turn the core on for this one.

 

[kathryn]

Whatever hurts the most, 'cuz then I know it's effective!

I like using med balls (actually, Ooof balls) or Smartbells when doing abs, and the stability ball as well.

 

[catwoman]

Anything that works my obliques! I don't know why, but I love working my obliques.

Otherwise, I like the pec decs (spelling?) in the Leaner Legs ab section, and the 3-part reverse crunches in the beginning of the same workout (upper, lower, both, and release).