Tighten your midsection (sucking your gut to your spine) whenever possible to strengthen your transversus abdominus. If diet and stress are in check, abs shouldn't take long at all. I just vary it up, but one day I'll do something like situps on an abs board with a 10 lb medicine ball until failure and then at failure, perform torso twists at the peak of the concentric movement until failure. Failure = absolute failure. Coming short of failure is pointless, that's why I only advocate HIT training, not volume training. I used to do that lame old s**t of like... 5 sets on flat bench... let's just warmup with a 45 on each side, sit around and b/s, do another set with a little more weight, blah blah, it's frickin pointless. Do the workouts like your going through an obstacle course trying to save the life of the girl of your dreams. You go to each exercise without rest, you perform it until you can't do another rep... you conquer it and move on. As far as abs... pick 2 things... smash the hell out of your abs and move on. Do em until you can't breathe and you're about to cry.
As far as other things, hitting the heavy bag and tightening the abs while you throw upper jabs and body shots will give you a good midsection workout. Rodja's Tai Boxing alone would probably upkeep his midsection even if he weren't to do a targeted ab exercise again.