I bought the Venzo from Amazon because it was highly rated on various bike forums. I see it's out of stock at the moment, but I paid $59 shipped.
Amazon.com: VENZO Bicycle Bike Torque Wrench Allen Key Tool Socket Set Kit: Sports & Outdoors
Interestingly, as SpeshulEd says above, after you use it a few times and get a feel for how tight things should be, you will probably seldom use it. It's worth the price, though, for peace of mind on that expensive carbon!