I just bought a icharger 106b+, these things are incredible. The manufacturer was involved in RC message board during the design and testing faze. There is over 700 pages back and forth http://www.rcgroups.com/forums/showthread.php?t=839657 You can update the software and do graphs. With an external resistor you can do up to 170W discharge tests. Their factory calibrated and considered very accurate. Their about $100 shipped from the usa at EPBUDDY.COM Their are some others at about $60 that do most of the same stuff but their not nearly as reliable as the icharger.
I just bought a digital tester from Radio Shack. It cost $29 or $25 (don't remember) and I had a coupon for $10 off, so I figured I couldn't go wrong. I really like it. It is not real fancy but it is digital which is what I wanted. The testing range covered all the batteries I use . . . And it is small, so it fits easily into my lite /battery/ other important things box.
I bought two ZTS MINI-MBT testers from BatteryJunction for under $30 each. ZTS makes battery chargers for NASA.
One of them has been doing yeoman duty for years at a local cabaret where the sound tech tests and sorts all batteries (by remaining capacity) before they are loaded into body mics. The club has saved hundreds and hundreds of dollars by knowing exactly how much they can get out of each cell before depletion.
Search for ZTS with the Google search box at CPF for more info. It is a very powerful tool and depending on what you use it for it may pay for itself very quickly. I've never heard a bad word about one.
ZTS tester is a completely different type of tester than whats mentioned above. ZTS will only tell you approximate state of charge. The above mentioned devices, iCharger and CBA will tell you the actual mAh capacity of a cell at various discharge rates. I personally have a CBA III and I like it quite a bit. I may pick up an iCharger in the future as well....
I use the ZTS for quick tests to see if a cell is charged and how much the approximate charge level is. For more detailed performance testing I use the CBA-3. Great tool and it really shows you how a particular cell is performing.
One other charger you need to consider if your budget is tight. The Imax B6 you can get them for around $25+ $10 for a power supply. The only real limits are a 1A discharge rate and you can't connect them to a computer but for the price mine served me well.