Amp is kind of the "standard," Sargent make a good unit as well. If you don't expect really heavy use (all day every day), the ones sold at Home Depot are pretty decent (for ~US$30.00).
If there's any variety-of-use, you can get crimpers with changable die sets...so they're good for RJ 4x, RJ11, 14, handsets (whatever RJ that would be)....The changable dies are also nice, because the dies do wear out with age (or work themselves to mis-alignment)....then you can buy new dies for $30-35.00 instead of a new (high-quality) tool for $65.00.
Most commercial electronic supply places will have a selection. The Radio Shack crimpers are crap for heavy use (OK for occasional use, but you can do better for the same money).
FWIW
Scott