Logon Security

I am from a small town where IT is not near as demanding as the big city. However, I still believe in security. I have seen businesses in the big city use these devices that are on a keychain that tell the user what their password is at that time. I am not sure what these are called or how to set them up. I will gladly do the research if someone can direct me in what they are called, and maybe where a good place to purchase them are! I have two branch offices that are using a VPN between the offices, and the users are logging in from home also. We want to make sure that the users logging in from home have a little more security. Any help would be greatly appreciated!