Limitation highlight of SQL server editions

The following applies to SQL 2005 Editions.

Feature	Express	Developer or Enterprise	Workgroup or Standard
Is free?	Yes	No	No
Redistributable?	Yes	No	No
Work with Team Foundation Server?	No	No - Developer Yes - Enterprise	Yes
Concurrent Connection	5	No Limit - subject to @@MAX_Connections	No Limit - subject to @@MAX_Connections
Database size	4 GB	No Limit	No Limit
CPU supported	1	Maximum OS supported	2 - Workgroup 4 - Standard
RAM Supported	1 GB	Maximum OS supported	3GB - Workgroup Maximum OS supported for Standard

Others features comparison list can be found here.