I go to the gym on Mondays, Wednesdays and Saturdays. On Tuesdays and Thursdays (or Fridays, depends how I feel) I will go for a run in the morning and do some Ab work later in the day. I feel like if I had a good Ab routine then I would get a lot more out of my workouts. Also, I could easily up the number of times I work my abs from two to three times a week if need be.
I would still classify myself as a beginner though so try to keep the exercises simple and if possible doable without any equipment.
Any help would be greatly appreciated and rewarded with vote ups! :)