There's a building around the corner from me that I always notice, because they've got these sexy little floating numbers on the front of it. They're a bit more work to install than hanging a placard, but they sure look a damn sight better.
Although 185 there is the only guy in the neighborhood rocking these, I started poking around and found that floating house numbers are more common than I thought. Both Home Depot and Amazon sells this Hillman Group variant pretty inexpensively at six bucks per digit.
On the more expensive (and garish) side, Luxello LED sells a back-lit variant that's aluminum up front, acrylic in the back, for $57 per digit. And I imagine these are a pain in the ass as you've got to wire each numeral separately.
Etsy seller MidwestSalvageStudio sells pretty, nickel house numbers mounted to salvaged boards, but it's not clear if they actually fabricate the numbers themselves, or are just sticking store-bought ones onto their reclaimed wood. Either way the results are nice-looking.
Chris over at Curbly did something pretty cool: He made his own using Extira, a waterproof MDF, and painted them up to look like metal. "Minus drying times," Chris writes, "the whole project took me about 1 1/2 hours and cost around $19. Can't beat that."