Hi Mike!
I use an air body saw purchased from Harbor Freight - Trent Bosch recommended this for doing some major saw-sculpting; it's one of the tools he uses in his 'vessels of illusion' series.
I also own the 400,000 rpm Powercrafter unit that takes 1/16" friction fit burrs - it works great, but these high speed "drills" don't have a lot of torque -so don't expect to hog-off lots of stock with these - they are finesse tools, good for piercing and thin-wall sculpting. Binh Pho uses one of these high speed air tools (although he uses an NSK) as his main carving and piercing tool once he has turned and dried his thin-walled vessels. I also know that J. Paul Fennell and Andi Wolfe use these kinds of tools in a lot of their piercing and carving.
For the bulk of my power-carving, I prefer to use a Foredom Tool - the 'standard' SR version of the hung-motor flex-shaft tool - it's not an air tool, but extremely versatile. I have about 5 or 6 Foredom handpieces of different styles. I'd recommend this tool as a starting point. Much better for carving and related tasks than the generic Dremel tool.
Several people also use air-driven dental drills - Malcolm Zander uses one of these with great success. You should look-up his web site to see what can be done with a dental drill, some great ideas, and lots of skill. I am very impressed with his turned and pierced pieces - especially his lace series.
Good luck with your tool selection!
Rob Wallace