I like to rummage for sheet music in second hand stores and op. shops. I have quite a sizeable collection of music now, and it's great for sight reading, or saving for 'one day'. Like Elspeth, I prefer second hand music, there's something warm about it having belonged to someone else-and good if there are pencilled notes! I 've also picked up a few pieces on e-bay. Islamey for $10 recently-that's definitely in the 'one day' pile.
My best find was in the local op shop which keeps a box of sheet music out the back, so you have to ask one of the little old ladies to get it for you. More often than not there's nothing worthwhile, so then you have to give the box back for her to put away for you. One day I went and there were the Beethoven sonatas (Corder) and the Chopin Nocturnes (Peters). Very old, but in perfect condition. Quite nonchalantly, I asked her how much, and she said ,would $5 be alright? I think I may have thrown the money at her, grabbed the books and ran out of the shop before she changed her mind. I hope she didn't think I was rude!