Sure, there are many DB monitoring tools out there, but Ignite focuses on tracking, analyzing, reporting, and explaining wait events within the database--and you'd be amazed how often waits caused by your code, that of others, or from other operations in the DB are the explanation for poor performance. It can help target exactly what SQL statement or other operation is a cause of significant waits.
The tool presents the data aggregated over time, so you can view it per hour, day, week, etc. Great for both drilling down to find hot spots, and for viewing how coding/config improvements (resulting from your responding to the analyses) have led to performance improvements over time.
The tool runs with low overhead: it reads data that the DB provides, storing it in a database and providing a web-based interface to view that data. The process to read the data and create the repository (and present the web-based interface) can (and should) be done on a server separate from the server being monitored.
Here's a nice 2-minute demo. There's also a free trial, of course, and it's pretty quick and easy to install and benefit from.
As I noted in the title, it works with SQL Server, Oracle, DB2, or Sybase (sorry, not MySQL. Don't know why). And while it's a commercial product, it's not a ridiculously high price (as for some tools). I just learned of it in the past few weeks, and one customer of mine who tried it has been just thrilled with the results. I hope to write more about it later, but wanted to at least get this info out for folks to consider.