I would probably buy four Maxi-jet 1200 powerheads. They pump right around 300gph, which means that with four running they'll turn over your 72 gallons about 17 times per hour, which is probably about where you want it if you're doing a reef tank (I think most people recommend a minimum of 10 times per hour, but some say as much as 20...I say split the difference). Do more smaller units rather than fewer larger ones to get better random flow.
Oh, depending on how much flow you put through your filters, skimmer, etc, you could go with somewhat smaller powerheads (I have the maxijet 600s in my 28 gallon tank...silent, reliable, nice). But I don't think you can go wrong with making them a bit bigger, particularly if you're going to use a wavemaker, which will be shutting some of them on and off, thus reducing overall throughput.
On the wavemaker, I can't help you! Haven't researched those yet.
By the way, you can get maxijet 1200s for about $17 each.