Most small engine work I use a Craftsman 3/8" bending beam torque wrench, think it's 0-75#/ft. The fine print says torque wrenches are only accurate in the top end of their range so you don't want to use a 0-250#/ft wrench on rod cap bolts that are supposed to be 25-30#/ft.
For tightening the nut on the flywheel I use my Digitork 0-250#/ft 1/2" t-wrench.
Also, the Craftsman "lifetime Warranty" does not apply to torque wrenches.
There's other good brands, Proto, Snap-on of course, S-K, Kobalt I've heard good things about, even ALLEN. Recalibration is available locally in most bigger towns/cities, ask a local mechanic or look in the yellow pages and call around. I've seen descriptions on the internet of how people check calibration themselves very easily. Biggest thing you can do to keep a torque wrench in calibration, is what Kevin & Jeff said, but also, NEVER loosen things with a torque wrench. Very good friend of mine who was a heavy truck mechanic for years told me that. SON & I were the ONLY people he trusted around HIS tools because we tool as good of care of them as He did. His MAC roll-around was FILLED wth Snap-on tools, S-O stopped warrantying his S-O roll-around's because the weight of "STUFF" He had in it. I'd guess his roll-around weighed close to 3000#. Probably worth around $50,000.