[efoote868]

Require new accounts to receive at least some positive reputation before they're allowed to create a new thread, which is where most spam goes.

If all of us veterans know about this policy, I'm sure we'd be more than happy to keep an eye out for new accounts and rep them for making any contributing post.

If it isn't too difficult, you could also have a 30 day waiting period for the account to do something relevant to a legitimate user, such as using the search function or browsing through several threads.

The point is that these simple methods could deter automated spammers, but wouldn't be too much of a hassle for a human user. And if it is a human that is setting these accounts up, there isn't much you can do to prevent it; although you could get more moderators to police the forums for spam.