Avanti! and The Private Life of Sherlock Holmes... beautifully written gems that don't always get mentioned in Wilder discussions.

I've never seen Fedora, though they say it was not too good. Also, I haven't seen Buddy, Buddy since catching it on HBO in the mid-80's. I do recall it being quite funny but I was 15 so, y'know...

Neither are on DVD, unfortunately.

If you like Billy Wilder, then rent Billy Wilder Speaks (2006). Here's the NetFlix description:

In 1991, filmmakers Volker Schlondorff and Gisela Grischow spent two weeks interviewing Hollywood legend Billy Wilder about his life and versatile career. In this intimate documentary portrait, the acclaimed director relives moments from his 50-year career, from his early days as a screenwriter in war-trodden Germany to his place as an undisputed master of the cinematic arts, all told with honest enthusiasm and charming wit.