If you are doing cardio for longer than 20-25 minutes (and not lifting on the same day), you are WASTING YOUR TIME.
20 minutes of HIIT will do what 60 minutes of cardio does and also give you an afterburn effect.
Read about it here:
http://www.musclemedia.com/training/hiit.asp
Also, remember that abs are made in the kitchen, not at the gym.
Eat healthy.