Best Marathon Anime?

I like a good shonen for marathons. I had a great time marathoning the 54ish episodes of FMA:B that were out on my spring break last year. Code Geass, TTGL, Baccano!, Durarara and generally balls-to-the-walls anime are a lot of fun.

And you can't go wrong with the classics. GitS, Cowboy Bebop, etc.