Yes, check out "Mr. Blandings Builds His Dream House" - a great film with fine performances by all. Douglas in much younger and of course - sharp as a tack. Here's the IMDB link:
http://www.imdb.com/board/10040613/?ref_=nv_sr_1

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Besides the films already mentioned, I'd recommend The Candidate, The Americanization of Emily, and especially I Never Sang for my Father.
Douglas was a treasure.

Douglas was a wonderful leading man, who made up for not being the handsomest man in the room by being the most charming and witty. He was a lot like William Powell. I loved him in "Ninotchka," and "Theodora Goes Wild."

This guy had been around since the 1930s but I never really noticed him as an actor until this film in 1979. As brilliant as Sellers was, Melvyn Douglas was equally brilliant and heartbreaking in his role as Rand.
Douglas was cast as the dashing leading man in lots of 30's and 40's films. Many actors who got such parts in their youth didn't have any careers to speak of in middle age or beyond because once their looks went, there wasn't much left. Douglas had the talent to carve out a niche for himself even in old age.
One of Douglas's other good late supporting roles was as a Senator and heir to an ill-gotten family fortune in
The Changeling
(1980 horror film starring George C. Scott).

I was going to mention Blandings as well. That little break in his voice when he's wryly delivering a zinger - can't be beat. Can see why Blandings would feel threatened by his wife's relationship with this humorous, intelligent, charming man.

He was great in this role. One role I liked him in was Mr. Blandings Builds His Dream House, opposite Cary Grant and Myrna Loy. Though the movie has such an odd title, it was very funny with great performances all around.