Strangely enough, I have just spent the past day or two researching torque wrenches for bike work. I eventually decided I needed at least 2, ideally three.

Firstly, a low-range wrench, around 1nm-20nm range:

Apparently this wrench, although a generic design and widely re-branded, is decent: Wiggle | X-Tools Pro Torque Wrench and Bit Set One Size | Workshop Tools

And this one, also generic and re-branded, is not as good (note flat section near the head, and silver head pin): Wiggle | LifeLine Essential Torque Wrench Set | Workshop Tools

Secondly, a larger one, around 10nm - 100nm. Here in the UK, we have Norbar, who make some very nice looking torque wrenches.

Finally, one of the key-type ones (eg, the Park Tools adjustable), for convenience when working on CF frames.

I then found this discussion:

Torque wrenches - why I don't use them for bikes: Triathlon Forum: Slowtwitch Forums

Essentially concluding that, due to the large variation in the condition (clean/dirty/lubed/chewed up) of the bolts being torqued, a certain applied torque results in a huge range of clamping forces (which is what we are really trying to set).

At this point, I gave up, and decided to buy a shiny new allen key set instead.