The following is a collection of articles for the Microsoft SQL Server platform which contain SQL that you may find useful for creating alerts in your environment.  You can enter the SQL in the Custom Alerts SQL text box as described in Alert on Performance Metrics.

Alert on IO Usage of SQL Data Files

• SQL Server 2008: I/O Wait Time per Database File
• Data File I/O from the SQL 2008 Activity Monitor

Alert on Log Shipping Related Errors

• Different Ways to Monitor Log Shipping
• Log Shipping Monitoring and Status

Alert on Log Space Availability

• Monitoring SQL Server database transaction log space
• SQL SERVER – Monitoring SQL Server Database Transaction Log Space Growth – DBCC SQLPERF(logspace) – Puzzle for You
• Monitoring SQL Server Transaction Log Growth Using DBCC SQLPERF(logspace)
• All Databases Data & log file size, space used & free space
• Monitoring Transaction LOG Space on SQL Server

Alert on Real Time Transactional Replication

• Monitoring Transactional Replication in SQL Server
• Transact-SQL Script to Monitor Replication Status