In keeping with the blue and white theme, I'm tempted to go with blue and white china vases for the flowers. I'm still partial to hydrangeas, but considering some sort of white flowers too. So here are the basic ideas:
Blue hydrangeas in plain, white vessels. Something clean and low, and simply elegant.
Something delicate and white, with just a touch of dainty blue - evoking a colonial feeling, perhaps. I especially like this for a historic venue.
Or my latest "oooooh" moment. An almost oriental vase, white with tons of beautiful deep blue patterning, overflowing with a single type of bloom - probably sticking with white flowers to keep it from getting too busy. I feel like this looks the most elegant (but that might just be because I love the feel of this inspiration photo!).