I have a confession to make... I don't train my abs. I trust that squats, deads, and sandbag work will hit my core plenty.
However, I feel inclined to point out that there are no such thing as lower ab exercises. your abs contract as a unit or not at all. And since I don't think my ab training (or lack there of) is appropriate for fighters, I'll tell you this, when I DID do ab training I did one heavy exercise at the end of each weight training session with a lot of emphasis on things like saxon side bends, full contact twists, bent presses and the like. These are exercises you cannot do without weight. if you wanted to, you could alternate low rep (which I define as less than 10 per side for abs) and high rep (20 or more) from session to session.
My big fear is that since you said "upper, lower and side" is that you're using shitty exercises. so what are you planning on doing? cause eljabo's routine (550 reps on a heavy day?!) sounds like a big steaming pile of horse shit to me. so does that fucking t-mag article... here are some better ones:
http://www.angelfire.com/hero/urbandruid/Strength_training_101.html My first "article" complete with a section on abs
http://www.t-nation.com/findArticle.do?article=205abs (even though I've lost a lot of faith in davies these are great exercises)