What is your favorite mod?

I can't believe I blanked on them in my own reply, but to piggyback off your Restoration Project nomination: the Talking Heads Addon and Talking Heads Actually Talk Mod for Fallout 2 Restoration Project (updated) are both absolutely insane, and breath some new life into the game while seamlessly slotting in next to the existing art and voice acting.

I love mekanism, often run it as my only mod