If you are interested in some of the issues involved in true (context and 
scope-correct) IntelliSense rather than just simple 'completion lists' 
(which many editors provide), you may be interested in this article which 
goes into some of the parsing problems we've had to solve in order to 
implement the Ruby In Steel IntelliSense:

http://www.sapphiresteel.com/IntelliSense-in-depth

best wishes
Huw Collingbourne

http://www.sapphiresteel.com
Ruby Programming In Visual Studio 2005