The list of UCI approved non-standard wheels is here:
UCI List
I've heard rumor that USAC is going to bring their equipment rules into line with the UCI rules over the next couple years, but haven't really checked to verify.
I still race on an old pair of the Specialized tri-spokes-- they're still legal for track because the non-standard wheel rule only applies to mass start road events. I agree that they're bomb-proof, having crashed them a couple times. They still have some of the best aero performance available, though they're also about the least stiff aero wheel you can buy. Most of the time the squishyness doesn't matter, but there are a few events where I'd like a stiffer wheel, so I'm looking at maybe getting some 404s.