What particular implementation can be recommended?
Win32Forth is really fantastic, as mentioned above. It has a nice integrated development environment and is a pretty modern implementation that seems to match up very well with the standards as well as including some more experimental but widely-accepted features.
I use Gforth, but I also use Vim to edit source files. :) Gforth is good and "classic" as far as the features it supports. It gives you a very "old school" Forth experience without being overly quirky to use. (Some free Forths do odd things with their command lines and such - I use Brodie's "Starting Forth" as the model of how a Forth interpreter should behave.)
I looked at SwiftForth, which is a very nice "high tech" Forth system that goes well beyond what the classic Forths offer in terms of language features and really brings Forth into the modern programming world. If you want to actually do Forth programs professionally, SwiftForth looks like it can handle just about anything you want to do with it.