My server at ev1 is at 400GB right now. I won't be too surprised if the usage is over 700GB/month in six months. Most of the bandwidth is binary download.
I have some options
1. Get additional dedicated server.
2. Replace with two servermatrix servers w/ vlan. vlan means more flexibility in the future.
3. Replace with a 10mbit dedicated server.
I dont know if your still interested in opinions but take a look at the MRTG for your server and if you see it going above 10MB (or even 8) you probably dont want to go for the 10mbit dedicated server (unless they allow you to burst , which isnt very common)