Curaga announced in this forum thread the open-source RadeonTop utility. RadeonTop allows for monitoring of undocumented performance counters on Radeon graphics hardware from the R600 series and newer.
RadeonTop provides a look at the percent utilization of the graphics pipe, it also provides percent-based numbers on the usage of the event engine, vertex cache, vertex grouper + tesselator, texture addresser, texture cache, shader export, sequencer instruction cache, shader interpolator, shader memory exchange, scan converter, primitive assembly, depth block, color block, and clip rectangle.
For open-source Radeon graphics enthusiasts, this is a useful utility worth checking out. RadeonTop code is available from GitHub while the discussion is taking place in this forum thread.