If you have an android smartphone, I *highly* recommend the free Aedict app, based on EDICT.  You can input kanji through either handwriting, or via radicals, and the best part is, you can look up kanji compounds too ^_^
The interface is really easy too.

I don't really know if I would buy a denshijisho... I have my fabulous app, and it's good enough for me.  You might feel differently though. ^_^

The Casio models are very popular for Japanese students and foreigners learning Japanese. The top of the line Casio model provided the green goddess dictionary both eng-jap & jap-eng, nhk pronounciatiation dictionary, and lots of other great stuff. But there is a lot of stuff bundled that is useless. You can buy a lower model and subsequently add propietary dictionaries but they are expensive and I read they can be a bit awkward to use vs. using pre-installed dictionaries. I have limited experience with the Casios so others will be able to add more value here.

That said, I think the Casios are made for Japanese so they are not too useful for foreigners with limited Japanese skills. They are also bulky (and expensive if you want to have a variety of dictionaries).

I use some dictionaries on the iPhone; convenient as phone is always with me. Be warned that the iPhone does not recognize kanji character input (huge fail by Apple). You can use Chinese input but this misses a lot of Japanese words. Writing with you finger is also painful; you can't use any fine pen to draw in detail, just a fat finger or special fat pen.

For the iPhone imiwa is a good free dictionary app. The dictionary is decent but the interface and conjugations were well thought out; impressive. There are a few dictionary apps that have a Japanese kanji input engine (that works only for said programs); those are discussed on this site recently.

My main dictionary is the Dell Axim x51v. It is a PDA (!) with a great kanji input system and small enough to carry in my pocket, although it is not svelte. It uses EB Pocket as a dictionary app and I upload dictionaries. I use this as an electronic dictionary and have some Japanese databases on excel (eg heisig keywords). Microsoft just Crushed the kanji input software for Windows Mobile 6.x; the kanji input is superb and an absolute pleasure to use.

Actually also I have EBPocket on my iPhone and desktop, all running the same dictionaries. It is a good solution but for great Kanji input, I rely on the Axim.

The guy who sells the Axims and related software also recommends the Samsung Galaxy Note. The Galaxy provides great features in a modern android platform. Getting Japanese Kanji input to work in Androod is also a challenge (Google fail) but links below and some links at RTK site can help.

If you have a Nintendo DS, there is a Japanese-English dictionary program that sells used for about 2000¥. It has good kanji input. But it is only one dictionary and not spectacular. The kanji input is excellent although the screen is a bit small and low resolution.

Some of the following site info is dated but the site is a good resource. There are advantages to buying software that is not locked into one device.
(I am not affiliated with the following site)

http://japaneselanguagetools.com/GalaxyNote.html

http://japaneselanguagetools.com/bus.html

http://japaneselanguagetools.com/docs/other_dics.html

In the end I purchased an economical dictionary solution and used the extra cash to buy some good textbooks and reference sources (Grammar dictionary series, pronounciatikn guide, JLPT books...). If I outgrow my current dictionary I will update that. Cross that bridge when it comes...

Good luck!

I myself have a CASIO-EXWORD but as for this moment, it's quite useless for me. When I was studying in Japan, it was incredibly helpful, especially when there was no Wi-fi available. My favorite part about the dictionary is its Kanji dictionary and how most definitions has so many example sentences with a quick English translation. When I got back to the states, I found myself using a internet jisho instead as it saved me more seconds then typing/writing it into my electronic dictionary.

I think you would like to buy the dictionary if you're going to any institution that perhaps requires a Japanese electronic dictionary (language school), or going to Japan. But even if you are going to Japan you may not need it.

It's mainly for convenience.  I happened to pick up the Casio XD-D9800 recently on ebay which has that green goddess dictionary.  It's the same one you can get for android or iOS if you have EBPocket or the like.  The keyboard and the jump features make it easier to navigate.  I happened to get one for which I think was a good price ($160).  I haven't looked through all the contents yet but it is a pretty neat device.

People have varying opinions on the utility of 電子辞書.  I have a Casio XD-B10000 and I use JEDICT on my laptop.  The JEDICT is acceptable for reading, more or less, but for writing, it's largely useless.  The sample sentences and better definitions in the Casio are key for me.  If you could try using a 電子辞書 for a bit, you might see whether your Japanese skills are good enough for it to be useful.  I haven't tried any of the apps for phones yet, although I probably should.  I like having a keyboard for rapid entry, but that's a personal preference.