SQL server Release - Version information

SQL Server 6.5
6.50.201 - SQL Server 6.5 Release To Manufacturing (RTM)
6.50.213 - SQL Server 6.5 Service Pack (SP) 1
6.50.240 - SQL Server 6.5 Service Pack (SP) 2
6.50.258 - SQL Server 6.5 Service Pack (SP) 3
6.50.281 - SQL Server 6.5 Service Pack (SP) 4
6.50.415 - SQL Server 6.5 Service Pack (SP) 5
6.50.416 - SQL Server 6.5 Service Pack (SP) 5A

SQL Server 7.0
7.00.623 - SQL Server 7.0 Release To Manufacturing (RTM)
7.00.699 - SQL Server 7.0 Service Pack (SP) 1
7.00.842 - SQL Server 7.0 Service Pack (SP) 2
7.00.961 - SQL Server 7.0 Service Pack (SP) 3
7.00.1063 - SQL Server 7.0 Service Pack (SP) 4

SQL Server 2000
8.00.194 - SQL Server 2000 Release To Manufacturing (RTM)
8.00.384 - SQL Server 2000 Service Pack (SP) 1
8.00.534 - SQL Server 2000 Service Pack (SP) 2
8.00.760 - SQL Server 2000 Service Pack (SP) 3
8.00.2039 - SQL Server 2000 Service Pack (SP) 4

SQL Server 2005
9.00.1399 - SQL Server 2005 Release To Manufacturing (RTM)
9.00.2047 - SQL Server 2005 Service Pack (SP) 1
9.00.3042 - SQL Server 2005 Service Pack (SP) 2
9.00.3042.01 - SQL Server 2005 Service Pack (SP) 2A
9.00.3054 - SQL Server 2005 KB934458 Fix
9.00.3152 - SQL Server 2005 SP2 Cumulative Update 1
9.00.3175 - SQL Server 2005 SP2 Cumulative Update 2
9.00.3186 - SQL Server 2005 SP2 Cumulative Update 3
9.00.3200 - SQL Server 2005 SP2 Cumulative Update 4
9.00.3215 - SQL Server 2005 SP2 Cumulative Update 5
9.00.3228 - SQL Server 2005 SP2 Cumulative Update 6
9.00.3233 - SQL Server 2005 QFE Security Update
9.00.3239 - SQL Server 2005 SP2 Cumulative Update 7
9.00.3257 - SQL Server 2005 SP2 Cumulative Update 8
9.00.3282 - SQL Server 2005 SP2 Cumulative Update 9
9.00.3294 - SQL Server 2005 SP2 Cumulative Update 10
9.00.3301 - SQL Server 2005 SP2 Cumulative Update 11
9.00.4035 - SQL Server 2005 SP3
9.00.4207 - SQL Server 2005 SP3 Cumulative Update 1

SQL Server 2008
10.00.1600 - SQL Server 2008 Release To Manufacturing (RTM)
10.00.1763 - SQL Server 2008 RTM Cumulative Update 1
10.00.1779 - SQL Server 2008 RTM Cumulative Update 2
10.00.1787 - SQL Server 2008 RTM Cumulative Update 3

Knowing your server's version and product level information
Execute the below query in your Query analyzer or Management studio
SELECT  SERVERPROPERTY('productversion') , SERVERPROPERTY ('productlevel'), SERVERPROPERTY ('edition')

To know other properties available : SERVERPROPERTY