Google, in cooperation with the Stop Badware Coalition is now alerting people when the link they’re wanting to go has a reputation for spyware/malware.
They also have a page where you can submit pages that you discover with malware on them.
Tuckerfan, is this working now? I tested it when they first announced it, and - a big resounding nothing. I got straight onto a site stuffed with undesirable things, no warning, no nothing.
When I emailed them to ask if the project had actually been launched, I only received an automated reply. 
AFAIK it is. I don’t know how many sites they’ve got tagged as of yet, and I haven’t had a chance to test it, but from what I understand they’ve gone live with it.
If I understand their site correctly,the sites they have tagged are listed in the right hand block on this page: http://www.stopbadware.org/home/reports
But if you access these sites through google, no warning, no nothing.
Let me know if you get around to testing it and it works.