You didn't say what your use of Certificates is. If they are for employees, you can, of course, just create your own. Employees will have to do a one-time install into their computer's Certificate store.
If this is for non-employees, you may want a commercial Certificate. If you only need secure communication to a web site, you can use the cheapest commerical Certs. If you intend to collect money with the site, you'll probably want the "verified" Cert, as mentioned above, which gives a stronger verification of your identity to your customers.