I will keep this post short as I guess that most of the peoples reading this know where to go and who to meet.
From my experience:
Chamber of commerces events (you might see the same peoples every time, so it might not extend your network)
Embassy related events
Networking clubs (like Paris Club in Japan)
I would however recommend to join events organized by headhunter or recruiting companies. For example Robert Walters organizes such events few times a year. You might benefit by meeting your peers, also potential candidates and also keep in touch with recruiters (might help your career at some point)
Finally, for peoples enjoying fine food, eating in restaurants, clubs and so on might make you close to very privy peoples.
Final (promise) point, my best connections happened in the park I go every weekend with my kids…