What the SQL Server performance tools do better than Activity Monitor is aggregating data and highlighting outlier behavior.

ApexSQL Audit: Offers a tamper-protected auditing tool that can be configured to monitor SQL Server for changes in configuration, schema or data.

Redgate Software is launching a new version of its SQL Server monitoring tool to enable accelerated analysis of SQL Server problems. The platform, SQL Monitor, is a web based SQL Server alerting and ...

To enable organizations to get the most value out of any database, anywhere, Redgate SQL Monitor now offers support for SQL Server on Linux.

Redgate is launching upgrades to its SQL Server performance monitoring tool, strengthening its query tuning and optimization functions to facilitate enhanced query identification, optimization ...

Google for "SQL Monitoring tools" and you get plenty of hits for products that can watch the actual DBs, including transactions, locks, etc. That may or may not be what you are looking for.

Ok, so my current company has no real monitoring, at all (yes, I know). It hurts. We are, thankfully getting SCOM 2012 soon, so general OS monitoring will be taken care of for perfmon type ...