Electronic dictionaries are good because they can help you look things up quickly when you are on the go, and they often have a few tools to help you study. However, most Japanese-English electronic dictionaries are designed for Japanese people, so some of them cannot be used well unless you already know kanji. It is important to find a dictionary that is “foreigner-friendly”, meaning that you can use it even if you do not know how to read kanji (yet).
I have owned two electronic dictionaries in the past. Both of them were Canon Wordtanks. However, the last time I bought an electronic dictionary was in 2001 and they have changed a lot since then. It used to be that Canon was the only one that foreigners could use, but now there are lots of choices. (And I am not sure if the current model of the Wordtank is still foreigner-friendly.)
If you are thinking of buying an electronic dictionary, you might want to try asking around to see what people are buying these days. A good place to ask about this is TAIRA, a local mailing list that includes about 1000 members. There should be a few people on the list who have recently purchased an electronic dictionary and who are willing to give you advice. This topic comes up on TAIRA every now and then, so you can also look in the archives for some general advice.
Advice about models
* Japan Shop (Since this shop is mainly for people who are not already in Japan, you might want to use this site to compare models and then buy the one you choose at one of the local electronics shops.)
* Electronic Dictionaries: A Buyer’s Guide (Dated, but still useful.)
* How to Choose a Good Dictionary (Mainly for paper dictionaries, but some general points to consider.)
* Article on Kanji Dictionaries in Alien Times