Everytime I visit new city I want to know places where all hackers/startupers/bright minds hangout. That is why I decided to create (and update over time) the list of places I personally visited over years. This list includes coworking spaces, cafes etc.
In the heart of Silicon Valley Red Rock cafe is the place to go. Most visitors there will be people talking about technologies, startups. You will meet hacker, investors there.
St. Oberholz is an amazing place in Berlin. It's great cafe with proper food and coffee. It has two stores and very working-friendly. It's place for hackathons, meetups and just meeting point in Berlin tech scene.
Another good option that I like in Berlin is mobilsuite coworking space. Some good meetups are using this great space.
There is amazing group of technology enthusiasts in Rio. Guys from group meet every week and work together for one day. They are super passionate about open source and different cool technologies. Henrique Bastos is the guy to meet there. He will tell you a lot about technology in Brazil.
If you are in capital of Ukraine just go to coworking place Chasopys. It's has good location, lot of rooms and bunch of cool residents. You definitely can meet lot of interesting people who are in technology.
I'm going to update this list with time. If you have some good recommendations send me Pull request and I'll try to visit place and add it to my list.