747b0392__5_1___Postgres_OnLine_Journal__Microsoft_SQL_Server_2008
[Feature] Can program stored procs/functions in multiple languages [MySQL 5.1] No (except C and Pl/SQL) [PostgreSQL 8.4] Yes - PostgreSQL just does it the cool way (common ones PL/PgSQL, sql, PL/Python, PL/Perl, PL/R) - we like having our code right there where we can see what it is doing. Downside server must host the language environment. It now supports variadic functions similar to Oracle. Neither MySQL nor SQL Server support that. [Microsoft SQL Server 2008] 
Yes - In theory any language that complies with CLR -e.g VB.Net, C#, IronPython - but you need to compile into a dll first and then load the dll into the database. The dll is stored as part of the database and the dependencies registered in the SQL Server GAC - a real PITA if you have lots of these dependencies than are non-standard.
Cross Compare of PostgreSQL 8.4, SQL Server 2008, MySQL 5.1 - Postgres OnLine Journal
Microsoft SQL Server 2008