What is the best thing you have ever made with leftover green beans? I only have enough for a one dish meal or an appetizer. Thank you!

Green bean bruschetta.
Brush sliced baguette with olive oil, grill.
Saute them with some garlic, olive oil, salt and pepper. Once cooled, throw them in the food processor with some ricotta cheese, lemon juice and some basil if you have it. Add more EVOO/seasoning depending on your taste.
Add mixture to grilled bread and top with parmesan :)

If they aren't too cooked, I have sometimes made a Thai green papaya salad. If you can't find the green papaya, use thinly shredded cabbage. All that is then required is the Thai viniagrette and maybe some tomatoes and mint or Thai basil.

You could add them to a cold gazpacho soup in place of, or in addition to, cucumbers. They'd also be perfect in a chilled Nicoise composed salad.

If you have time, these fried beans sound like a tasty appetizer with some ranch dip. http://food52.com/recipes/19813-deep-fried-green-beans

Might not use them all up, but since it's basil season - pasta with pesto, green beans and potatoes is really good (traditional in Liguria, home of pesto.) Here's Mario Batali's version: http://www.mariobatali.com/recipes_trenette.cfm I use whatever long, skinny pasta I have around.