Our company, Staff.com is run by different virtual teams from across the world. We are at around 80 people in 9 different countries.
Here are some of the tools we use to communicate and collaborate:
Skype/Google Hangouts - for meetings (audio/video). We also keep an open chat on Skype where everyone is around. That way we could keep an informal conversation going on. Very essential especially if your people are telecommuting.
JIRA - great for issue tracking. Greatly used by our developers.
Jing - sending instructions to virtual teams using chat is sometimes not enough. Jing helps us illustrate through screenshots and video.
Google Drive - Google Docs and Sheets make everything collaborative.
Time Doctor - excellent time management software and is probably the most important tool we use. It allows us to monitor our work time while at the same highly encouraging productivity.
As to company culture, communicate a clear mission and vision to the whole company.
Make sure to overly communicate this from time to time. Everything you do should revolve around this culture.