Hello there EJ,
First, check out our glossary page on antonyms, which contains some examples:
http://www.usingenglish.com/glossary/antonym.html
I had a quick search for you, and came up with a couple of online dictionaries that give antonyms:
http://www.synonym.com/ http://vancouver-webpages.com/wordnet/ http://thesaurus.reference.com/
And if you want to look for more dictionaries that I have missed out, here is a great place to find them:
http://www.yourdictionary.com/diction1.html
I hope these help, and if you need any further help or advice, please feel free to ask!
Regards,