He's my 2nd favorite director.
The Major and the Minor (1942)
Double Indemnity (1944)
The Lost Weekend (1945)
Sunset Blvd. (1950)
Ace in the Hole (1951)
Stalag 17 (1953)
Witness for the Prosecution (1957)
Some Like It Hot (1959)
The Apartment (1960)
One, Two, Three (1961)
Irma la Douce (1963)
Most of these titles require no explanation. The 9 in the middle are essential.
With The Major and the Minor, you see Wilder develop his style. It's starts very clunky, almost painfully so. But it grows into what you call a typical Wilder screwball farce.
Irma la Douce shows Wilder at the start of his decline. All the Wilder trademarks are there in the writing and directing, but he pushes things a bit too far. It's busier than it needs to be, ultimately feeling stretched kind of thin.
If neither of these approaches interests you there's always The Fortune Cookie (1966), which is considered by many to be Wilder's last really good film. I, however, didn't like the film much and think it's only memorable for being a Lemmon & Matthau team-up as well as the film which won Matthau an Academy Award.