Microsoft has released SQL Server 2008 R2 RTM Cumulative Update 2 (CU2) today. It became available for download today, and you can request it here. This is Build 1720, and it includes 18 fixes, mostly for Analysis Services and Reporting Services.

Below is a SQL Server 2008, SQL Azure, and SQL Server 2008 R2 Build List.

-- SQL Server 2008 RTM is considered an "unsupported service pack" 
-- as of April 13, 2010
-- SQL Server 2008 RTM Builds     SQL Server 2008 SP1 Builds
-- Build       Description        Build        Description
-- 1600        Gold RTM
-- 1763        RTM CU1
-- 1779        RTM CU2
-- 1787        RTM CU3    -->      2531        SP1 RTM
-- 1798        RTM CU4    -->      2710        SP1 CU1
-- 1806        RTM CU5    -->      2714        SP1 CU2 
-- 1812        RTM CU6    -->      2723        SP1 CU3
-- 1818        RTM CU7    -->      2734        SP1 CU4
-- 1823        RTM CU8    -->      2746        SP1 CU5
-- 1828        RTM CU9    -->      2757        SP1 CU6
-- 1835        RTM CU10   -->      2766        SP1 CU7
-- RTM Branch Retired     -->      2775        SP1 CU8
-- SQL Azure Builds
-- Build            Description
-- 10.25.9200        RTM Service Update 1
-- 10.25.9268        RTM Service Update 2
-- SQL Server 2008 R2 Builds
-- Build            Description
-- 10.50.1092        August 2009 CTP2
-- 10.50.1352        November 2009 CTP3
-- 10.50.1450        Release Candidate
-- 10.50.1600        RTM
-- 10.50.1702        RTM CU1
-- 10.50.1720        RTM CU2