When I’m reading, I sometimes run across a word I know, but I’m not quite sure how to pronounce it. Well, either of these sites will solve that problem, and more.
The MacMillan Dictionary. I personally prefer the pronunciation on this site, plus it tosses in a thesaurus, word of the day, buzz words, sample sentences, and tells you how often others use the word.
The Oxford Dictionary. Pronunciation is not quite as clear. However, it offers the Text Checker, a compilation of 3,000 words chosen by language experts for their usefulness and importance. You can do a cut/paste of your text into a box and get results that will tell you how difficult your text might be for someone reading it. Considering that many people read at the 5th-8th grade level, this could be important to any presentation you might be making. It also gives examples of how the word is used.