I followed the github meteorirc project\'s lead and put them in /public/
I installed my node modules via npm from inside /public/ and therefore I have a /public/node
Meteor takes lib/node_modules from the development bundle and makes a symbolic link or copies it to server/node_modules, which is in the hidden .meteor sub folder under your project.
So, if you cd into the lib directory of the development bundle or into server directory of the .meteor folder (I believe it is in build); you will be able to use the node modules. If you have trouble loading them, you might want to check out this question.