I finished Fallout 3 yesterday. I am going to install the 5 DLC's from the GOTY edition and start the game over again. What an awesome game!
I also downloaded the Unofficial patch for it(it fixes bugs not squashed by the official 1.7 patch) and am looking for a good weather Mod. I want to have rain(like in Oblivion), snow, fog, sandstorms, etc. as that would add a great level of ambience to the game.