Voices by Richard Lortz.
It takes one set (heck, all you need is a door pretty much), and has a cast of five. Granted, three of the parts are quite small, but the two leads have really great dialogue and the play's really well-written.
It's a pretty intense drama about a husband and wife whose son accidentally died a couple of years ago. The wife was so distraught she attempted suicide, and although she's recently been released from a sanitarium, the husband doesn't think she's all there. They take a weekend trip to a cabin where they're snowbound, and the wife starts hearing voices.
The show's very intense for the two leads, and there's a lot of really good back-and-forth between the two. Plus it runs about forty minutes and takes no set changes.
"You mean what was the best picture of the year or what did they pick as the best picture of the year?" - California Suite