We had a server with Rackshack for less important free sites and I won't even go into all the trouble we had with them...
www.isprime.com have managed servers with premium bandwith and great support staff. I can really recommend them
With their september special, you can get a server with 10Mbs for only $777/month.
It's extremely difficult to say what say what server configuration you will need considering the scripts though. Best add as much extra ram as you can to any package you choose.
Good luck with your choice