I have looked around on Google, and I have found tutorials on how to initiate a workflow from a custom action in the ribbon, but I have run into a problem. I am not sure why (I assume I have a setting wrong that isn't mentioned in the tutorials) but the drop-down under 'Initiate Workflow' in the Custom Action creation dialog contains no workflows at all. I have tried creating test workflows of both site and reusable types. I have several existing workflows that are associated with this list, and I have tried creating test list-associated workflows as well. Does anyone know why I wouldn't be able to see my workflows here?
EDIT: I have no idea what the problem was, but I used the URL location of the initiation form, and now the 'Initiate Workflow' drop-down shows my workflows. Guess it fixed itself...