PerformanceTest is a commercial application, but it gives you 30 days to try it out. It uses a synthetic benchmarking model that tests the CPU, graphics, memory, hard disk and CD speed.
The program gives you scores for these five components plus a combined PassMark score, but also provides more detailed information for most of those components.
For the graphics system, for example, there are individual tests for 2D lines, 2D rectangles, 2D shapes, 2D text, 2D GUI, 3D simple, 3D medium and 3D complex. This way you can learn something about the relative strengths and weaknesses of a particular component.
In addition to testing your own PC, there are several baseline systems for which scores have been provided, enabling you to compare your system to others in each category. This information is displayed via bar charts, making it simple to compare results.
Unlike some benchmarking applications, the software is easy to use, and unless you've got a particularly old system, running the tests will only take a few minutes of your time.