There aren't many options out there that are strictly abs. In my opinion, you can work the abs thoroughly in 20 minutes or less. Any more, and it's just overkill.
Trainer Edge - Killer Abs and Back - is a good one by Michael Olajide (sp?). The first half is standing work, then a short jumprope section, then on to the floor. I think the total time is 40 minutes.
The workout that give me DOMS is the bonus workout in Seasun Zieger's Rock Steady Step. She starts with killer plank work and then moves on to variations of crunches. I also have Fitball Upper Body and that is about 40% core work done on the ball. Lots of new moves and variations - I feel it but good the next day!
Hope that helps!
Diane