Before choosing the right edition, you may want to know that there are many versions:
– Enterprise Edition
– Standard Edition
– Workgroup Edition
– Web Edition
– Compact Edition
– Express Edition
– SQL Server 2008 Express Edition.
– SQL Server 2008 Express with Tools.
– SQL Server 2008 Express with Advanced Tools
Basicly it comes down to a few mind breaking features.
The Enterprise Edition offers extra/extensive features like:
– To work with large amount of data (terabyte-style or billion-row fact-tables)
– More BI features available (such as parallel processing, cube partitioning, and text mining)
– Less downtown (by using online indexing, fast recovery, etc.)
– Replicate data from Oracle (if you want to)
But….the Standard Edition is significantly less expensive than the Enterprise Edition.