Hi Jon,
I've used several types of pH meters. My current opinion is that the best for our purposes are the ones made specifically for gardeners and nurserymen like those made by Kelway and Myron L Corp- see
http://userweb.cybernex.net/kelway/ph.html and
http://www.myronl.com/products/agrimeters.htm for details.
Most pH meters that work (forget the really cheap ones as bad info is worse than no info at all) require a lot of maintenance - calibrating and conditioning - and can still be difficult to get a good reading from. The ones made for agriculture use such as the ones above are far easier to use and require little maintenance.
Good luck and please let us know your experience with whatever you try.
Charlie
