If RSpec is too slow to wait on you could use autotest, which automatically runs tests when a file is saved. There's also a plugin for it that uses growl/libnotify to display the results.
The solution is to use Spork to have a Rails test environment running permanently (it also does caretaking between sessions) and then RSpec will access it over DRb. Couple this with a good .watchr file to run only the relevant specs when you update them and you get very quick RSpec tests. It's a bit of a pain to set everything up but it's worked great for me.
http://www.rubyinside.com/how-to-rails-3-and-rspec-2-4336.ht...