The Decades Challenge is by far my favorite reading challenge. I don't know if there will be one for 2010 but I hope so.
For whatever reason my trickiest decade this year was the 1920s. It strikes me as odd because I normally read a ton of books from that era. This year though I kept missing either finding a book from the 1910s or from the 1930s.
The book that finally let me declare myself a winner was Arrowsmith by Sinclair Lewis. I loved his books when I was a teen but it's been about fifteen years since I last read anything by him.
The oldest book I read (actually re-read) was Don Quixote de la Mancha and I had fun posting my progress as I made my way through the book.
As you can imagine, my list is top heavy, with most of the books coming from the 1990s.