I've heard many say, "the only accurate way to test is underwater weighing." However, dual-energy x-ray absorptiometry (DEXA) is becoming increasingly popular. It not only gives fat and lean body mass, but bone density measurements as well.
Like pwr_machine, I use a university one. I know the university sometimes uses volunteers in studies or in testing/calibrating the equipment. If you live near a university that offers one, you can check into that. Also, they tend to do it for less money if you are having other tests done. I get a caliper, hydro, DEXA, and most recently a BMR test for about $50 bucks. They also cut me a break if I refer people or take people with me.