ruby-prof is a fast code profiler for Ruby. Its features include:

* Speed - it is a C extension and therefore many times faster than the standard
  Ruby profiler.
* Flat Profiles - similar to the reports generated by the standard Ruby profiler
* Graph profiles - similar to GProf, these show how long a method runs, which
  methods call it and which methods it calls.
* Threads - supports profiling multiple threads simultaneously
* Recursive calls - supports profiling recursive method calls
* Reports - can generate both text and cross-referenced html reports
* Output - can output to standard out or to a file

WWW: http://rubyforge.org/projects/ruby-prof/