I love ThisService because it lets me "script" MacOS X using the command line. It allows you to take any script and turn it into a MacOS X service. Scripts that take standard input make the most interesting services in my opinion. In any application, you select the text you want as input to your script, press the keystroke you've assigned for your service, and your script is invoked with the selected text as its input. Combine that with a python script using the webbrowser module like I have and prepare to triple your productivity(*).
(*) May also result in nuclear meltdowns.