Jisho is an excellent online dictionary for English speakers. One of its most amazing features is that you can basically throw at it anything, and it will try to help you: voice, drawings, English words, Japanese words (either in any Japanese writing system or using the Latin alphabet) and even full phrases!
But for this reviewer, perhaps this most interesting aspect is how Jisho pulls together a bunch of free culture projects to deliver an amazing product. It uses the JMdict, Kanjidic2, JMnedict and Radkfile dictionary files (CC BY-SA), Tatoeba example sentences (CC BY), the System of Kanji Indexing by Patterns, or SKIP (CC BY-SA), kanji stroke order diagrams from KanjiVG (CC BY-SA) and last but not least, Wikipedia (CC BY-SA). Jisho is a great testament to the power of a free commons.
Having said that, it is with a heavy heart that one realizes that Jisho itself it not free-as-in-freedom. The developers have freed some related tools used in the making of the website, but not the thing itself, which is quite disappointing. It’s that one dent that forbids this reviewer from giving it a full five star rating in an otherwise impeccable project.