It's like a yard of weeds: you kill one generation and the next comes back twice as strong. I've been trying to find a way to help others with spam, and the only method I've found, is http://www.google.com/safebrowsing/report_badware/ or http://help.yahoo.com/l/us/yahoo/search/spam_abuse.html
for yahoo or http://www.google.com/contact/spamreport.html another google one.
Other than that, Cloudflare.com offers "bad visitor" protection for sites you host with them.
Gmail's got a nice spam filter, since it learns every day from people reporting stuff as spam.
But unless it's causing YOU problems, let others deal with it on their own. You might make the spam sites angry and they might somehow conspire against your inbox. Trust me, though they are making email vaccines, they don't prevent every type of spam yet. There are only a few doctors that cure spam. Only spam back if it makes you less angry.
Other than that, make your web app less vulnerable: Include some sort of "verification" to get the message sent. Captcha is a very nice solution.
Best to you.