There are so many possibilities you'll have to use other criteria to narrow down your search such as price, availability, and plausibility. Narrow yourself down further by specifying if you want stuff like serviceability from the company who installs it (warranty and tech support), what your price range for spending (open source? corporate unix/linux?, windows?). Do you have the facilities for this server? i.e. an internet connection and other connecting computers? If so, what do the other computers run on them for software...and what type of cable connection do you have.
Just know that when you design a network that all of these questions should have answers and that if you do go with a company to network you, they should ask ALL of these questions and more. If they don't, they're only after the money and don't care about servicing you as a client. Get me some more info and I'll hook you up with an estimate.