Wordnik

Wordnik is an online resource which you (whether you are a native English speaker or not) might find useful. It is something of a multipurpose English dictionary. So far they claim to have a database of 1.7 million words, but it is an expandable database where users can add definitions, pronunciations, notes, tags, and related words. Wordnik draws upon a number of other online databases to compile each entry.
The example above is looking up "eschatology." (Click on the graphic to see the page for yourself in full size.)
What you will find are some example sentences where the word occurs. (Click on the Examples heading to get even more.) The examples I find came from quite a few different sources. They even include "real-time examples from Twitter."
The definitions are drawn from the American Heritage Dictionary, Century Dictionary, Webster's 1913 unabridged, and WordNet. Pronunciations come from the American Heritage Dictionary, but you can record your own. A statistics graph attempts to chart how often the word was used in a particular year (going back to 1800) and the "unusualness" of its use. Related words are suggested. (I created my own free account and added "apocalyptic" as a related word to "eschatology.") Images tagged with the word in Flickr are displayed. (Apparently a little Flickr humor that some rearends of cows and horses are included...) You also get etymologies from a couple dictionaries.
There are, of course, quite a few online English dictionaries, e.g., Wikipedia, Encarta [via Bing], Merriam-Webster, Answers.com [which draws from a number of other dictionaries and encyclopedias], Dictionary.com [which also draws on a number of sources], wordiQ, KartOO [which is rather unique in its presentation and definitely worth checking], and more. Add Wordnik to your bookmarks.
[HT: Downes]