Lighting diagrams are very handy tools when you plan to do a portrait shoot, or any kind of shoot where you need to know exactly how to set up your lights. And there are plenty of websites that does this job on the web, or psd templates if you prefert to play with photoshop, or even apps for your phone / tablet.
And while I was searching for one of these sites around the web, I found this interesting website: Sylights. On this site you can create on the fly lighting diagrams, like many others does, but I have to say that unlike the others, with this tool you have much more control in the space you can use, a much more complete list of items to put in the diagram, and a lot of options that most of the other sites don't have. Plus it has a gallery of other users photos with related diagrams, which is really helpful for whoever is learning how to use studio lights. Plus if you register on the site you can share your diagram, you can save it an image and more.
So it's definetly a site to bookmark on browser, and I hope I will be able to use it myself soon!