The traditional ways of networking is to attend conferences, troll alumni networks, and participate in industry events such as pitch competitions.  While those are all fine and often effective ideas, the best way to meet potential investors is through referrals. Build relationships with other entrepreneurs & Founders of funded startups, who are often happy to introduce you to their investors.
Shervin Pishevar, Founder of SGN spoke to our TEC class of 2010 last week on this exact issue.   On the topic on networking, he said encouraged the interns to approach people fearlessly.  “You are in charge of your future. Don’t ever be nervous to approach someone to ask them a question. You are your biggest supporter, and you should embrace that” (courtesy of VodPod intern Ali Shah.)

I had a lot of success with volunteering with the local angel organization.  Many investor organizations are member-led and their members are always too busy with other ventures to pay too much attention to the administrative details of running an investment group.  So if you volunteer to do some of the grunt work, you can network with a lot of angels very quickly and they get a sense of your commitment to not just helping yourself, but also helping other people in the ecosystem (including other entrepreneurs).