I like nastursiums too! Did you know that the blossoms are edible in salads and stuff? A slightly peppery taste. Didn't even know this until last summer.
Also I love the black eyed susan VINE. BTW, Looks nothing like a black eyed susan. I found out this year that they are easy to grow from seeds in hanging pots and great for trailing planters.
Ohh, also I love the ornamental sweet potato vines, Bright green (DIS green in fact), varigated and deep purple (almost black). These really add a nice accent to planters! They grow like crazy!
I guess I don't have just one. I still have a list in my head !