Are you LinkedIn yet?
LinkedIn is a great way of connecting with dormant customers, past colleagues, old friends, influencers and potential clients. It should automatically appear in your web browser, when you wake your computer up in the morning. (You can achieve this, by using 'tabbed browsing'). When you make an interesting new contact in, say, Facebook, check to see if they belong to LinkedIn.
Joining groups is a great way of building your network. An example of a large LinkedIn group is LION ( LI Open Networkers), run by John L. Evans, which has over 19,000+ members. Once you've joined a group, you will be able to connect with any of its members, without knowing their email addresses. This will help you to find useful contacts.
Testimonials and recommendations: the best way to get these is to give them! From a marketing perspective - this is part of 'social proof' (i.e. other people saying how good you are). This is much more believeable that you saying...