I know someone, who shall remain nameless, who, when about to move out of their early 20th century walk-up apartment, absconded with all of the flat's period glass door knobs. In (somewhat) defense of the renter, s/he did replace them with standard metal door knobs from the hardware store. This was back in the '70s, so the replacements could very well have been seen as an upgrade. Seriously, though, is there anything more eye-catching in door hardware than a glass knob? You can still buy replicas of those the renter stole--you know, the ones that look like huge diamonds?--but if you're hankering for a more contemporary alternative, here are some stunners.
The Bubbled Glass Door Knob, pictured above is from Anthropology ($32) and comes in olive, clear, mint (shown) or pink. Note that hardware is NOT included.
Here's their bubble version, also for 96 bucks.
Speaking of impressive, Out of the Blue Design Studio's glass door knobs are nothing less than amazing, and they're made in the USA.