I've searched for something like this in the past without success and I was thinking to develop something by myself, but today I've discovered that Jamie Thomson, John Rayner and their team developed a Vista sidebar gadget to monitor a SQL Server instance.
Here's the gadget working on my local db in my notebook:
This is an interesting project (great work guys!) that I'd like to be extended in the future with other major or minor features. For example, the first minor feature to add is the possibility to search for a SQL Server instance and for a SQL Server database automatically by choosing the instance from a combobox. Actually you've to remember the names and type them manually...
And why not having the possibility to launch some SQL commands (T-SQL) inside the selected database? Why not having the possibility to monitor also a selected table inside the database (indexes for example)?
I've lot of ideas to share if the team is ready to listen... :)