BodyMax
I still think BodyMax has some very tough and thorough abwork.
Also, the abwork in CTX is exceptional - the abs on the end of Leaner Legs is unsurpassed.
Have you had any luck with FIRM tapes? Their "More 5-Day Abs" is very good. At the end of their Cardio Step Mix is a 6.5min ab section that just demolishes me everytime.
Karen Voight has some great abwork, too - the 12min in StreamLine Fitness is very very challenging.
Keli Robert's Abs & More is very good.
I always have to put in a plug for an oldie-but-goodie, Kathy Smith's Ultimate Stomach & Thighs. Outstanding.
Good luck!
Dawn P.