The following actions can also be used in nautilus or any other file manager that supports custom actions. I personally prefer thunar because of speed.

If any of the actions don't work anymore (especially the upload ones), please report here, so I can fix it.

This action converts any image file to a png image. (Should also work with layered PSD files)

This action converts any image file to a jpg image. (Should also work with layered PSD files)

This action pops up a zenity-based window and displays encoding information for and audio or video file.

This action pops up a zenity-based window letting you choose from your gpg recipients and encrypts and signs the file with your chosen gpg key. (Asymmetric encryption)

This action pops up a terminal window for password entry and decrypts the file with your private gpg key. (Asymmetric encryption)

This action pops up a zenity-based window and displays information about the encryption of the current file. (Asymmetric encryption)

This action pastes a text file to gist (in private mode) and pops up a zenity-based window displaying the paste url (shortened). Additionally the paste url will also be copied to clipboard.

This action uploads an image file to imgur and pops up a zenity-based window displaying the upload url.