With all due respect, I strongly disagree. Those small cheap ones are very inaccurate, and you really need to spend closer to $250 used or $850 new. This one is pretty good; my doctor has a professional version of this, which is about double the cost:
Tanita TBF-300A body comp. Scale - eBay (item 300418440775 end time Apr-23-10 10:06:03 PDT)
However, the only true measurements are the "bath tub" type, where you are dipped in water. That's obvioulsy only for a competitive pro.
Charles