I have the NewU game. The pilates section really targets your core! (But the rest of the challenges are a bit keen on pressups) If you want a cheap alternative, then the My Fitness Coach from Amazon for under £10 is good. You can key in core exs and you will work your abs. It's a bit repetitive but it works.
The My Fitness Coach Cardio (the boxing one) Is £10 on Play.com