SharePoint 2010 Build Number
Using PowerShell
PS C:\Users\MyName> $farm=Get-SPFarm
PS C:\Users\MyName> $farm.BuildVersion
Using Central Admin
Central Administration -->System Settings -->Manage servers in this farm
Configuration database version: 14.0.6120.5005
Configuration database server: MyServer\SharePoint
Configuration database name: SharePoint_Config_406d052a-1eca-4d94-b9c7-e54360977285
Using PowerShell
PS C:\Users\MyName> $farm=Get-SPFarm
PS C:\Users\MyName> $farm.BuildVersion
Using Central Admin
Central Administration -->System Settings -->Manage servers in this farm
Configuration database version: 14.0.6120.5005
Configuration database server: MyServer\SharePoint
Configuration database name: SharePoint_Config_406d052a-1eca-4d94-b9c7-e54360977285