When I went to canada for 6 months, I started lurking on couchsurfing.com even if I didn't need. Just to meet people. I met one good friend here, and I met her many times over here, and once in my country !
edit:
for Canada I also lurked a LOT on a special french website that is , in fact, like a giant forum with all related stuff to get there and live here. It helped me a lot (sorry I don't remember the website).
For India where I spent a year, I went with guys from my school so, I was not alone but we met people there that we contacted from the net. France (and maybe other people) have 'Alliance Française' in many country. It's a small organization run by France Gov which is here to help french guys abroad and give french lessons for foreigners. Many 'expatriate' blogs and website refer to this alliance française. So mainly I would say, there are like 2/3 major websites for foreigners (in specific countries) and most people meet from these blogs.