Do you need to terminate the fiber into the router, or is it an ethernet connection? Is this wireless or an interbuilding company reselling bandwidth?
If what you are saying is true about getting a 100mbit Internet connction, then you are talking about some serious bandwidth. Even two DS3's bonded together don't equal that.
In order to handle the load (assuming you will be using at least 50% of your bandwidth), you'll need to have at least a Cisco 7200 series router. If your connection is ethernet, you can get by with a relatively cheap Cisco 3550 layer3 switch. Basic Layer3 versions are around $2000 USD.