If you're serious about learning the language, investing in a Denshi Jisho is recommended, but if you're just going there for vacation and looking to communicate a little bit in Japanese, a traditional paper phrasebook or an iphone app will be great. C:
Denshi Jisho have the advantage of having about 100 different dictionaries indexed and searchable. You can also jump from one dictionary to another mid-search. (Very useful when needing to look up kanji, checking radicals or jukugo for one, or just jumping to a new word from the entry of another to understand it better. ++)
Depending on the brand and model, you also get "Native Speech" for many words. Many DJ only provide this for English words however, since the Denshi Jisho in almost all cases are aimed at helping Japanese people learn English, not the opposite.