Chopin's C# minor Nocturne.
That is one of the most gloomy pieces i ever heard.
I would play that when im sad probably

But if im ANGRY, the last thing i would play is the slow movement of moonlight sonata or C# minor nocturne, because to play them you have to be in a PATIENT mood, and when im angry im anything but patient

but i agree about 3rd movement of moonlight sonata when angry - (preso agitato?) its a good piece for anger because you can both express and take out your anger through the piano, bashing the keys and whatnot

When I'm sad, a few chopin waltzes, nocturnes 2 and 20, Debussy Arabesque No.2 (its very jolly

) and some short pieces by bach. like two part inventions no. 13(A minor), no. 1, no. 4 in F and the one in D minor. oh... and the 3 part invention in G minor. thats quite sad.