Finjan released SecureBrowsing, which is a browser extension than scan Web pages in realtime to detect potentially malicious content.
Some competing products and services rely on reputation-based systems, which are invariably questionable at best and can often be entirely misleading.
Finjan said that SecureBrowsing "scans each URL as it currently exists on the web each time the address is displayed in your browser."
If you're interested you can a copy free at Finjan's Web site