Canon Wordtank IDC-310
The Canon Wordtank IDC-310 is a brilliant little electronic dictionary. The main function is to translate English to Japanese and vice versa. You can also look up kanji based on reading, radical or stroke count, and look up words based on any component kanji.
Another useful function is that you can highlight any displayed kanji and look it up instantly. Unfortunately, you can’t highlight a compound and look it up — you can only look up single kanji in this way.
Still this is a must-have device because it’s tiny enough to carry with you everywhere (96mm by 60mm by 19mm, 83 grams). Best of all, it costs less than 5000 yen! There’s no English manual, but it’s easy enough to figure out even if you don’t know much Japanese.
Unfortunately, this model seems to be obsolete now — mine died, and I wasn’t able to find a replacement. Canon have made updated models though, so have a look out for those.