Campanula incurva
I saw this specimen at Annie's Annuals last June, and immediately began thinking about where I would plant one. The bells are a very pale, greyish blue, almost like smoke.
I bought my own in April 2006, and planted it at the foot of the quince tree (it really prefers a bright shade, but I didn't have much of that on offer; I may move it to a shadier spot if it seems to be suffering). It's still kind of looking like just a bunch of leaves, because it's monocarpic and won't bloom until next year (when it will also die). It's one of the few plants I've planted that is neither a perennial nor a self-sowing annual, but it's so lovely that I could not resist.
As a side note, when I was looking for the photo of from last year, I sorted through many many blue bell-shaped plants I made photo notes about. I guess I like them.
Campanula incurva is native to Greece, prefers rich soil, and average to low water. It grows to around 2 feet tall. It is hardy in USDA zones 8-10, so the rest of you just have to grow it in a pot.