You probably know Robin Wilson‘s list of free GIS data which is a great ressource if you search for specific datasets. He also is the creator of a blog concentrated on Python. But Karen Payne publishes a list which is quite impressive as well. The list of geodata links is taken managed using Google Spreadsheets and has more than 1000 links to different portals, data types and services. Unfortunately the categories are not that well structured in my opinion and the list is yet a bit US focused:
Conservation and Environmental
US State Repositories
Other portals of interest
You can view the whole list of geodata repositories here. Unfortunately the list is not editable online so you have to contact Karen via Skype or other methods as she wrote in the document itself. So enjoy this catalogue and send her your additional links.