When building a SQL Server, it is important to make sure you are selecting the correct version. To keep licensing costs as I can, I tend to recommend using the cheapest version possible while still accomplishing what you need to.
Here is a list of the primary versions you may see and a brief overview of each.
Enterprise ($$$$) – Full version of SQL. Used for applications requiring mission critical in-memory performance, security and high availability
Standard ($) – Slightly scaled versions of SQL. Typically used for mid-tier applications and databases
Web ($) – Web hosters and Web VAPs
Express – Free version of SQL
Developer – Non-prod use
If you are using Enterprise edition, make sure you need it and the cost difference makes sense.
Here is links to the most recent versions of SQL Server that describe what is available in each.