I know I said I wouldn't start with this one, but Davis-Kidd had it on the shelf for $10 so I watched Sunset Boulevard this afternoon.
I don't hear about this as much as I do some of the other film noir classics, but now that I've seen it that surprises me. Gloria Swanson stars as an aging silent film star who was unable to make the move into talkies but who devotes herself to planning a return to the big screen. William Holden plays the down-on-his-luck writer who agrees to help her with the script she's preparing. There are wonderful cameos by the likes of Cecil B. DeMille, Hedda Hopper and Buster Keaton, who play themselves.
Here's a trailer: