Third Down For What was a catchy tune with a really thick baseline, which combined with the "Third Down" part and a simple gesture the entire crowd could do, made it a hit. It was a fresh at the time -- I mean, people may claim the crowd's not into it anymore, but from my spot in the crowd during the Oklahoma game last year it sure looked to me like people were still pretty freaking into it.
It's hard to catch that lightning in a bottle, and harder to replace it. You need a certain rhythm, a certain beat, to get something like that working. I've yet to hear of a good replacement for Third Down For What. Most of the time folks suggest songs they personally like but are unfortunately either not catchy, not the right presentation, or just older tunes which don't connect with young people (and sometimes even older people).
Kill Third Down For What if people want, although I'll personally miss it, but don't try to stick something else in its place and make it work. You can't make something cool -- can't force it. Forcing it is how you get "Smokey's on the prowl."