I can back up the Ergo XTR grips, I've used them a few times on firing other 1911's. I really like them, I like all Ergo grips (like the AR grips). I can't say much about alumagrips except for a "They look like" comment, which is "They look like they don't come to par with what I'd like".
Also, ERGO, you can get from Wilderness Tac, like Gregs link said. They've got a store on Hatcher I frequently go to, to buy more and more surefire batteries, shirts and etc.