I haven't ever found a free one that was much good, simply because a good one is worth it's weight in gold
I've personally used Glowcode
http://www.glowcode.com/[
^] and Intel's VTune
http://software.intel.com/en-us/articles/intel-vtune-amplifier-xe/[
^] and would recommend them both
In my experience, efficient code, like secure code, is normally impractical to retrofit