I have read that while plug-ins are not supported for SQL Server Management Studio, it can be done.
Does anyone have any resources or advice on how to go about it using C#?
A company that is currently offering plug-ins to Management Studio is Red Gate: http://www.red-gate.com/products/SQL_Refactor/index.htm
Here’s a list of a lot of free tools for sql server. at the top you have the section that holds stuff about add-ins from SSMS.
You might also want to check out SSMS Tools Pack which is an add-in I made. It’s free but not open sourced.