Networking monitor

I havent recently came under control of a smaller company who is starting to have network issues. I have looked into a few networking monitor programs how ever I have not found anything that I like 100% yet. I was wondering what suggestions everyone might have for a smaller company, about 40-50 people. We do not host any servers in house we out source our server hosting. I am just looking to monitor network traffic and bandwidth to make sure no one is streaming anything.