I shoot IDPA, and I use either my Glock 19 or my Glock 21. I'd steer you to either of them (or almost any Glock, for that matter) with much confidence. The G19 is my carry piece as well.
A Kimber .45 ACP would be another firearm high on my list. I think they're the best out-of-the-box .45's out there without going to a custom shop.
Most of the guys you'll see doing well in IPSC are probably shooting a .38 Super.
If you plan to shoot a lot, I'd steer you to a 9mm based on ammo cost.