You can find all SAP tcodes at One-stop SAP Reference & Collaboration.
There are more than 100,000 tcodes there. It has the search function (based on tcode name, description, and its program) and shows the SAP menu path(s) for each tcode.
There are also additional information and links about the tcodes. You can also contribute by adding additional information and link of your favorite tcodes.
This link will take you to answers for similar questions on SAP Transaction codes.
Always a good idea to search the site first.