Wordnik.com is a search engine for words. More than a dictionary, but less than Google, this site hits a sweet spot for people like me who have a genuine interest in words. Here's the description from the site:
What is Wordnik?
Wordnik is a place for all the words, and everything known about them.
Our goal is to show you as much information as possible, as fast as we can find it, for every word in English, and to give you a place where you can make your own opinions about words known.
Traditional dictionaries make you wait until they've found what they consider to be "enough" information about a word before they will show it to you. Wordnik knows you don't want to wait—if you're interested in a word, we're interested too!
By "information," we don't just mean traditional definitions (although we have plenty of those)! This information could be:
• An example sentence—we have tons of examples and gobs of other data for most words. But even if we've only found one sentence, we'll show it to you. And we'll show you where it came from.
• Related words: not just synonyms and antonyms, but words that are used in the same contexts. Cheeseburger, milkshake, and doughnut aren't synonyms, but they show up in the same kinds of sentences.
• Images tagged by our friends at Flickr: want to know what a pout looks like? We'll show you.
• Statistics: how rare is tintinnabulation? Well, we think you'll see it only about once a year. Smile? You might see that word many times, every day.
• An audio pronunciation—and you can record your own!
• Something YOU tell us! Use the "Comments" and "Contribute" links to tell us something—anything—about a word.