Beethoven's Grosse Fugue is one of my all time favorites and I could probably spend a whole week talking about it, but since I'm currently travelling here's an interesting comparison between Beethoven's original string quartet version vs Wilhelm Furtwängler's orchestral arrangement. I play Ludwig's original arrangement much more often - but the Furtwängler is no slouch!
Grosse Fuge, Op. 133 for String Quartet
Pt 1-2 Quartetto Italiano I think
Pt 3-4 Furtwängler's orchestral version
Pt 5-6 Winkler version for fortepiano
Pt 7 - pour a good stiff drink.