The tried and true method is to pick up the phone and call a colleague, a competitor, or a customer and invite them to lunch at least once a week. Frequent your local "hot spot" restaurant and keep your ears open for side conversations.
But the Internet is making the whole concept of networking MUCH easier for us these days with a virtual explosion of social networking sites.
A new one on the scene, Gather.com, has "groups" of likeminded people forming. We have just formed one for Sales and Marketing. You can join here http://www.gather.com. Just navigate to our Sales and Marketing group to start more interesting discussions.
Friends of mine working to market themselves in the music business are having great success networking on Myspace.com.
There are new such sites every day, and I encourage all of you to NETWORK, NETWORK, NETWORK!