Thesaurus.com

http://thesaurus.reference.com/
When you perform a query on Dictionary.com, you're retuned with a search results page containing results from a number of different sources. Many of the individual results entries will contain the word's etymology near the bottom of that entry (e.g. Dictionary.com Unabridged etymology is reddish text, enclosed in brackets, and beginning with the word "Origin"). Also, you can scroll down the page and look for results from the Online Etymology Dictionary.