You can use the CRM Diagnostic Tool that can be downloaded from Codeplex. This is the same tool Microsoft tech support will have you run when you submit a ticket.
http://crmdiagtool2011.codeplex.com/
Run it and choose the troubleshooting file tab at the top and generate a report. As long as you are a deployment admin, it will pull all the environment information for the CRM environment.
It should list out the plugins. At least it did with the 4.0 tool. It will also provide a lot of detail that you may not expect.
It will not list out the jscript files on the forms though
Jason Peterson