If you only have the one account you can use the free program called Mail Washer http://www.mailwasher.net/index.php that will allow you to delete the spam before it is downloaded. (It can also be set to automatically delete)
If you have more then one account, (Or if you use Hotmail, Yahoo etc) then you will need to purchase the full version.
BTW all Antivirus and Firewall vendors (Norton, MacAfee etc) produce Anti Spam programs.
Hope this helps.

Bill