SQLFirewall is exactly what the name implies. It is a firewall for Microsoft SQL Server currently supporting SQL 2005 and SQL 2008.

What does it do?
1. Can log all queries against SQL
2. Can block queries before they reach SQL
3. Can log based on user or keyword
4. Can alert based on multiple indicators

Advantages
1. Transparent to End User Applications.
2. No impact to the SQL Server (If run on a separate physical box)
3. Ability to review a connection's or user's queries as they were run.
4. Logging for compliance.
5. Logging for security forensics.
6. Doesn't require proprietary hardware.
7. Very small software footprint.

Limitations:
* Limited to 5 users

The license of this software is Free Trial Software, the price is $299.00, you can free download and get a free trial.