What good open source tools are available for monitoring SQL Server 2005?
Tools available within SQL Server which I have used in past
SQL Profiler
DMVs
Perfmon
Is there any 3rd party open source tool available like IDERA – Diagnostics or Quest – Spotlight which can help you to evaluate the health of your SQL Server
My company, SentryOne, puts out a free query plan analysis tool called Plan Explorer. You can read about it here: https://sentryone.com/plan-explorer
And see this blog post showing off its many advantages over analyzing execution plans in Management Studio:
https://blogs.sentryone.com/aaronbertrand/plan-explorer-3-0-demo-kit/
Adam Machanic puts out a great little stored procedure called sp_WhoIsActive:
http://whoisactive.com
As for a full monitoring solution, there is an incredible amount of I.P. that goes into doing this – from collecting data efficiently to presenting it in a useful manner. So it is unlikely that you will find a comprehensive solution in the open source arena – but that shouldn’t stop you from sniffing around at sites like CodePlex or GitHub.