Much prettier than the name "Spiderworts" might imply, this is a perennial also known as Tradescantia. Looking much like a day lily as it grows, the flowers sprout from the joining of two leaves instead of on stalks. Each blossom only lasts a day. I've also just been given an annual variety called Purple Hearts which has a very dark purple foliage. I'll post pics when they grow and blossom.
For more on Tradescantias on Wikipedia, click here.