Winter '12 Force.com Platform Release
Developer Console

The Force.com Developer Console is a significant upgrade to the analysis and debugging tools available within Force.com. It's composed of a set of related tools that allow you to look at your source code and review how it executes. It can also be used to monitor database events, workflow, callouts, validation logic, and other events that are saved in debug logs.

Here is a blog post describing the new Developer Console in greater detail:

• New Developer Console in Winter '12