Originally Posted by Tent Pitcher

Daily visitors is not a good metric upon which to base server resources, it is way too subjective. Certified offers Webalizer and AWStats, both of which will tell you the exact amount of bandwidth your users are consuming along with the average bandwidth per user, etc.

Certified says they offer "unlimited" storage and transfer, but most hosting companies cap this at some practical level - like maximum transfer rate or maximum Gigabytes in a billing period. You should contact them to find out this number, then compare that to what your statistics are telling you to get a good idea for how close you are currently operating (or trending) relative to their limits.

Just as an aside, and I am not whoring their services, but Rackspace offers a completely dedicated server option on their Cloud Server platform that would run you about the same rate as what you are currently paying. You are charged based on bandwidth used, so you don't have to worry about hitting any caps. The only catch is that you need to be fairly computer (linux) savvy to take full advantage of it.