IPs matter. Having different Class-C's is what you're looking for. Idealy you should even have those different accounts on different servers rather than just having different Class-C's coming from a single MAC address on a server.
There are a number of hosts that do it, but what kind of budget are you looking at? How many sites, IPs etc?
Hostgator offers a form of hosting through
www.seohosting.com. There's a number of the hosting companies that frequent the forums here that also offer somthing similar, ourselves included. If you want information about us, drop me a PM or in the Marketplace so I can provide more details.