I have been playing around with the WOT browser add-on for couple weeks with good results. WOT stands for Web Of Trust, it is a community knowledge based system where information on websites are shared. After installing the add-on, the links from search engines are tagged with extra symbols showing whether the site's "reputation" level. Very simple to understand, red means potentially bad site and green means good site.

As you can imagine, lots of links to malicious sites flow through my mailbox every day, WOT toolbar was able to identify most of them (I only recall a few instances where it failed). On the other hand, some of the seemingly legit site seems to be tagged as dangerous but these are rare and I honestly didn't look too deeply as to whether they have real bad stuff or not. 

Overall, I would recommend it to average users as an extra layer of defense. Worthwhile to mention that it is available both in Firefox and IE. If you choose to use it, remember to contribute back to the project back by helping to rate sites as you visit them. Time to introduce my parents to this add-on.