I compared the tools from Idera, Red Gate and SQL Sentry. I found that SQL Sentry gave me:

- An executable client, eliminating the need for a web server

- A polling approach instead of having to install a monitor application on the monitored servers

- The ability to drill down to what statements were running at a point in time

- Integration with a great query plan tool plus a view similar to Oracle's explain plan

- A monitor for SSAS as well as SQL Server

I believe that the SQL Sentry and Red Gate tools are both excellent.

We chose SQL Sentry. Overall, I've found it to be a very good tool that I'd be comfortable recommending to anyone.