Single-boot heaven is what we've got here. La Sportiva only does boots, and their more-than-a-mouthful Trango S EVO GTX has been around a while and is still top of the line. I won't even try to list all the funky-named technologies they stuffed into these boots: they are lightweight, waterproof and take a combi crampon is what's what.
I reamed these suckers out on Rainier, bouncing them off rocks, ice and my partners head when he wouldn't shut up. Using the trusty ol' double-sock method - a thin liner sock under a medium-weight hiking sock - the only problem I had was a little heel lift that was easily solved by cranking down on the laces.
The Trangos took a lot of abuse and didn't flinch, with no malfunctions or even much visible wear. They give plenty of ankle support for a fifty-pound pack, and they climb like hyperactive goats. Comfy and warm, I've had no problem wearing these down to around zero degrees. A great choice for climbs and conditions that don't require a double-boot or a lot of vertical ice, and at a mere 3.2 pounds they won't slow you down.