I spent many hours struggling with this same problem! I could not get rspec to run within Sublime Text 2, using the Michael Hartl "Ruby on Rails Tutorial." It kept saying
/bin/sh: rspec: command not found
I finally realized that the RubyTest package (https://github.com/maltize/sublime-text-2-ruby-tests) was looking in the WRONG PLACE for my RVM! (Since you use rbenv, I will change my answer for this.)
On my Mac, the path for RubyTest is /Library/Application Support/Sublime Text 2/Packages/Ruby Test
First, to make RubyTest seek the rbenv, I changed the parameter in RubyTest.sublime-settings from
"check_for_rbenv": false, to "check_for_rbenv": true,
Then I dug into the Python code of run_ruby_test.py: https://github.com/maltize/sublime-text-2-ruby-tests/blob/master/run_ruby_test.py
At line 129, inside class BaseRubyTask, it had the wrong path for my rbenv:
rbenv_cmd = os.path.expanduser('~/.rbenv/bin/rbenv')
I changed it to the full correct path:
rbenv_cmd = os.path.expanduser('/usr/local/rvm/bin/rbenv')
If this is not your path, find the correct path by typing
"which rbenv" and substitute that instead.
After saving run_ruby_test.py, I went to Terminal, cd to my Rails application directory, and ran "spork"
Finally, I opened static_pages_spec.rb in Sublime Text 2. Now all the tests work from it!