Hi PianoDreamer,
Thank you for donating your time and talent to your local hospital. When my Dad was ill, there was a harp player that would set up her harp from room to room and play for anyone who happened to be in that room. My family and I really appreciated it - it was beautiful. She played mostly improvised new age type of material (in another words, kind of noodling within one scale or mode and then positioning her pedals on a new scale/mode to go to the next piece.
If you aren't comfortable improvising like that, or still would like to stay along the lines of classical piano, may I suggest the following easier but still original classical piano pieces:
-Gymnopedie #1 by Satie (anything by Satie for that matter!)
-Bach's Prelude #1 in C from the WTC Book 1
-Minuet in G by Bach (from Anna Magdalena book)
-The 1st section of Debussy's Clair de Lune (you can just skip to the end after the first page and half) no non-pianist will notice or care.
-Traumerei (Dreaming) by Schumann. Only 1 page in length, but it is a little tricky on the 3rd and 4th lines.
-Fur Elise (you kind of have to wait for a receptive waiting area audience on this one - I wouldn't play it if someone is visibly in pain or crying out loud for a loved one. You never know though, might bring back a good memory of THEM learning the piano.
-2nd movement of Pathetique Sonata by Beethoven (this is another piece where you could just learn the first part and maybe skip some of the development sections and finish up at the end with the recap).
-Minuet in G Major by Beethoven
-Chopin e minor prelude no. 4 (again, gauge your audience, as this one can get depressing)
-Chopin's short prelude in A Major no. 7(repeat the heck out of it!)
-Elegie by Massenet
-To a Wild Rose by MacDowell
-Mendelssohn's Venetian Gondola Song no. 6 from Songs Without Words
-and finally the first and last sections of Barcarolle by Tchaikovsky (it's in g minor)
You mentioned you play some Debussy. La Fille aux Cheveux de Lin (The Girl with the Flaxen Hair) and Arabesque no.1 immediately come to mind, although I would have to seriously look at and practice these again before I attempted to play them for anybody, as they are not so trivial reading-wise (The Girl is in 6 flats)and technique-wise (Arabesque).
One more thing I should mention - most if not all these pieces are in Borders Books and Barnes and Noble bookstores under titles like "Favorite Piano Classics - 83 Best Loved Works" or "The Piano Bench of Classical Music". I have used these books many times to brush up on all the well known classical pieces out there. Included in the books were even some pieces that were totally unknown to me and I ended up liking them and adding them to my repertoire.
Hope this list helps!
-Erich