Filtering Spam at the Local Level
The final line of defense against spam is your own email client. If you are using Thunderbird by Mozilla (http://www.mozilla.org) or Outlook 2003 or above, then the ability to have the email client filter out spam is built in. For Thunderbird, read the help section on "junk mail rules" for information on how to set up junk filtering. If you are using Outlook 2003 or higher (not Outlook Express), see this link for help setting up Junk Mail Filters http://office.microsoft.com/en-us/assistance/CH063564711033.aspx.
If you are using an older version of Outlook, such as 2000 or XP, or if you're using Outlook Express, then you can install SpamBayes to help filter out spam. Follow the instructions on the website to install and configure SpamBayes. SpamBayes must be trained by "teaching" it which are good emails and which are spam, but once it's been trained for a few days, it is remarkably effective in automatically removing spam from your inbox, and training it is very easy.
Finally, if you want to virtually eliminate all spam from your inbox without having to train a filter system, and are willing to spend a few bucks to do it, then consider subscribing to a challenge and response email service, such as SpamArrest. These services intercept all email sent to you, and respond to the sender with a message requiring the sender to click on a hyperlink to confirm they want to send you the email. Once a sender has confirmed they really exist (that is, they're not a spammer) their mail to you will go through without interruption. Challenge and response systems are extremely effective in eliminating 99% of all spam, but they require a one-time extra effort from your valid correspondents.