The '06 reign had a Race Face SRX ISIS bottom bracket, meaning you should be able to trade up to the current edition (
http://raceface.com/components/bb/52) and keep your current cranks. If you're looking at replacing those, then it's open slather, you can basically go with whichever crankset/bottom bracket pleases you. Personally, I like Shimano Saint gear, but I've also had Holzfellers from Truvativ and had literally zero problems after years of abuse.
Some background info to help with your confusion: Bottom brackets will generally come in three sizes: 68, 73 and 83 (for downhill bikes). Most bottom brackets are for 68/73 and come with shims or adaptors or clever designs that let you run your BB on either size. In your case, the SRX can run on either, so you should be fine with a direct upgrade.
As always, ask at your local bike shop if you're unable to work it out.