I used a really cheap "T2" cartomizer off eBay. This post is the rough tutorial I've followed previously. It's explicitly for a Ghostbusters implementation, but the basic principles will be the same!
http://www.gbfans.com/forum/viewtopic.php?f=2&t=36943
All credit goes to those guys for the idea - The most original thing I did was put some marshmallow smoke flavor in it .