80/120 will limit your chainring choice in future, but it's a standard SRAM don't look like they're going to drop any time soon, so availability will always be OK as long as your LBS has an account with Fishers.
Going for a conventional triple ring crank, with 104BCD, would open up running 2 rings with a bash for you as well though. And you can choose from all sorts of ratios of ring. With a 29er, your gearing is 10% taller than on a 26" bike anyway due to wheel size, so personally a big ring is totally redundant to me anyway. In fact, a 39T on the dual setup will be like a 42T outer on a 26" wheeled bike anyway.
24/36/Bash works well for me, I stay in the 36T for 80% of the time, downshift to the 24T early on climbs and run the chain half way down the block as much as possible, then slowly go up to about the 32T cog on steep/long climbs. The 36T really is an ultimate bailout gear with a 24T cog, really only used after many many hours in the saddle.
All I did to find various different cranksets was type "BB30" in the search field in ebay. Knock yourself out!