747b0392__5_1___Postgres_OnLine_Journal__Microsoft_SQL_Server_2008
[Feature] Graphical Explain Tool - no additional charge [MySQL 5.1] No (someone on Reddit mentioned maatkit visual explain for MySQL. This is still a text format though and not quite as pretty as SQL Server or PgAdmin III graphical explain plan. Are there others? [PostgreSQL 8.4] Yes - PgAdmin III [Microsoft SQL Server 2008] 
Yes - SQL Management Studio/Express
Cross Compare of PostgreSQL 8.4, SQL Server 2008, MySQL 5.1 - Postgres OnLine Journal
Microsoft SQL Server 2008