Sure, there are quite a lot of electronic dictonaries available. Although most of the ones I've seen are Japanese/English, not Japanese/American /ubbthreads/images/graemlins/tongue.gif
There are lots available here in Japan made by various brands including Sharp, Casio and Canon.
The Canon Wordtank is a very well known one - I have one myself, an IDF-4000 which is pretty good. The Canon US website doesn't seem to list anything about these products, but
this site seems to have lots of info.
Keep in mind, though, that these are electronic dictionaries, not translators. You enter a word in English or Japanese and it gives you the equivalent in the other language. They generally don't do phrases or sentences.
If you do a search in
Google for "canon wordtank" you'll get quite a few hits including places which sell them.
The other thing you can do if you have a PDA like a Palm or something, is look for J/E dictionary (or even simple translation) software for it.
Graham