You can start with this kind of site, because you will find that certain names keep popping up on the same pages you are visiting, and then you might exchange private notes via the profiles and ultimately that could lead to exchanging IM and email info and maybe someday meeting in person too.
I signed on to the iPling app for the iPhone but I'm having some technical issues with it... but it seems like a cool concept: you create "circles" based on particular interests you have, and then you can see the other people with those interests on a Satellite map image. You can then "Pling" someone from that screen just to chat and see where it goes. I'm hoping the reality is as good as the theory... but as a single 40-something who has tried online dating, I'm a bit leery, as well.
Like you, I want to meet new people and expand my social horizons, not just dating - although that would be nice too ;) So I, too, am seeking sites that might attract others with similar interests and mindsets as mine, as well as those that are related to topics that interest me in general.