In certain datacenters (think might be dallas05?) you can even get a 10Gbps uplink brought to a box so they have pretty big pipes available.
In Softlayer's Dallas facility (selected when ordering a server) 10 Gbps is an option.
The maximum amount of bandwidth available is 20TB.
Sometimes you can get more options by contacting their sales people directly instead of using the shopping cart.
In certain datacenters (think might be dallas05?) you can even get a 10Gbps uplink brought to a box so they have pretty big pipes available.