Hello Mark & Welcome
I imagine you'll get an overwhelming vote for Ryze.com - if you type Ryze into the search box here at the Forum, you'll find we've discussed it quite a bit over the last year.
Personally, I find it the best place on the net to make new contacts - whether they be clients, merchants, potential partners... or just friends. One of the best features is the ability to add a very detailed and personalized Profile - this allows you to really express yourself, say "who you are and what you do" with no restrictions, and so it also allows you to get a very good impression of each of the people that you meet as well.
In addition, their Networks, and the way that they rate them (most active and most members) gives you a clear idea of the type of people that are active on Ryze, and plenty of opportunity to join interest-specific or location-specific discussions.
Not only are they an international online business networking site - and the best, in my opinion - but they also have OFFline events and networking opportunities... There is tons of potential for the person that takes the initiative to set up their own Network on Ryze!
Personally, I've found it to be the single most responsive group of people online...