It depends on my current mood really...though there are a few peices that get me every time
Certain parts of Verdi's Requiem. The opening Requiem bit mainly, and the Lacrimosa too. The beginning of the Dies Irae just makes me want to go and hide behind the sofa though!
Vaughan Williams - Fantasia on a Theme by Thomas Tallis
Poulenc - The 2nd movement from his Clarinet Sonata
Wagner - The "Liebestod" from Tristan and Isolde. Truely amazing music
Elgar - Cello Concerto, pretty much the entire thing. Though it only really makes me cry when I listen to a Du Pre recording.
Bach - Certain movements from his Cello Suites can be quite emotional, depending on who's playing them. The Prelude and Sarabande to the 2nd suite are always like that I feel.
Shostakovich - Piano Concerto No. 2, 2nd movement
Gorecki - Symphony No. 3. There's this particular bit, about 17 mins into the 1st movement, where the original theme comes back. Even at the very least, it sends massive shivers down my spine.
"A Little Fall of Rain", from Les Miserables - Anyone who's seen the musical knows what I'm talking about...haha. We did a production of this at my school a couple of years ago, and members of the band were still crying on the 3rd night!
Radiohead - Motion Picture Soundtrack/Street Spirit (Fade Out)/Lucky/Fake Plastic Trees etc. They just seem to have this skill at writing very depressing songs, that are also very uplifting.
Well...that was quite a varied list
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