There are a few ways to minimise the risk, but there is no 100% solution, apart from not going on the web, the pro's may have further advice, but here are what I use on systems to minimise the risk, some are not completely reliable, so common sense is the greatest weapon you have, but between them they will help.
Host's File; adds known bad sites to you're hosts file, check the site for updates on a monthly basis.
SpywareBlaster; adds flash based risks similar to the Host's file previous.
SiteAdvisor; not always right, sometimes paranoid, but it explains why they list a site as bad, simple traffic light system added to you're browser.
WOT; similar to the previous, not always right, but they will make you aware they suspect an issue at least, but the issue is not always directly aimed at the specific site, sometimes it may find a link (often outside of they're control) somewhere on the site that leads to another site that has been known to have risks, so don't instantly panic when these flag up issues, take you're time too examine what it's telling you then decide if it is valid to you or not, hope this helps a bit anyway.
Another great tool, possibly the most essential tool for most, is
Iconix, this helps separate fake emails from real ones, especially where eBay\PayPal and banks are concerned, obviously the company (eg bank) you use has to subscribe to this service, it is free too you, and company's are signing up all the time, but it checks emails from subscribed company's and marks them as valid, or more importantly invalid (eg a scam), works with most all email clients AFAIK, even online ones like hotmail, so a great tool for most IMHO.