Which SQL Server 2008 Editions should I select?

This can be a confusing decision in many cases as this involves your choice of the technologies you intend to use and the budget your company allocates for upgrade or new system. Personally I suggest referring to below link to review the comparison of key capabilities between SQL Server 2008 Enterprise, Standard, Workgroup, Web and Express editions:

http://www.microsoft.com/sqlserver/2008/en/us/editions-compare.aspx

Do not select a higher and costlier edition for a system where you do not have any possibility of using additional features available with the costlier edition. However make sure to convey to all stakeholders about the limitation of choosing a lower edition as edition are not easily upgradeable with out attracting new license purchase.