That depends. ;-) There are several out there that I would consider at the top of the list, for SQL Server specifically: 1. Sentry One -
https://www.sentryone.com/ 2. Red Gate -
http://www.red-gate.com/products/dba/sql-monitor/ 3. Idera -
https://www.idera.com/productssolutions/sqlserver/sqldiagnosticmanager I personally like Sentry One, however both Red Gate and Idera have fully vetted and excellent monitoring tools. It really depends on what you want to monitor. All of the vendors listed above offer up some version of a trial that you can take for a test drive. I've been involved with all three companies in one way or another. They are all responsive to support issues and helping you get the most out of their respective tools. Others here might have other tools to add to that list. Hope that helps!