Hard to believe that only you (#62) and rightofrush (#72) mentioned my fav, Franz Joseph Hayden. I would recommend (demand) the piano sonatas, some of the quartets, and any of the symphonies. I listened to Symphony #100 (the Military) yesterday on the commute into work. I was ready to slay some Taliban when I arrived, if you know what I mean.
Also worthy of note, Shuman's trios.
Now that we're talkin Hayden, about 20 years ago when I was driving in New Hampshire with a lady friend, I heard a Hayden choral piece that was absolutel gorgeous and have been searching ever since. What was it? Guess--please.