I am more the offline data user but when it comes to the question “Where can I get my data from?”, Web Feature Services (WFS) are a great way to share your data with others. So where to find your WFS data? What catalogs are there? Follow me an find out.
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.