Sylights is another, more rounded and beautifully built lighting diagram editor. It comes as the standard web-based application and as a universal (iPhone & iPad) iOS app. To top it all the app is also free and can be downloaded here.
The website is extremely simple to use and has an extensive area of user-generated diagrams. These come with example shots and even some notes. The database of diagrams is searchable and can be filtered with many criteria. This makes it a good research tool, as well as a record of your own setups.
(via Damien Looney @ Little Yellow Jacket)