A report from the Center for Democracy and Technology analyzes how spammers acquire email addresses.
In short, they crawl the web for pages that contain email addresses as text. The report recommends breaking up email addresses by typing out "username at domain dot com" instead of the usual "username@domain.com".
full report
Presumably, a gif for the @ symbol would also work. The folowing links lead to a 10-point or 12-point @ gif. It goes without saying that they are public domain.
the gif
the gif sounds like a really good idea. if i was a spam bot designer, i would create a workaround that would look for text of the format "user at such dot com" and recreate the email address. after all, the spammers are already purposely mispelling words and throwing in random characters (have seen this a few times) to throw off email spam filters.
Charlie
cyberdash