Proper dictionaries are almost always better than their online counterparts, so I would suggest getting a good "physical" dictionary, but for online.. there is, as @azalea said,.. cantonese.sheik, but another nice up and coming site is www.zhongwenlearner.com.. its cantonese dictionary JyutDict is open source and translations are available for Cantonese-English, Cantonese-French and Cantonese-German.it also has input methods and a nice annotation tool. Hope this helps.