I'll start with this camera phone shot I noticed this evening in my travels:

October 4, 2009 - Round Lake Michigan
This next one is interesting because it has been sufficiently explained as caused by an extra-terrestrial source, a polar mesospheric noctilucent cloud resulting from exhaust particles spewing out of the experimental Black Brant XII Suborbital Sounding Rocket.

September 21, 2009 - U.S. Eastern seaboard
Anyway, I'd appreciate it if you'd please contribute if you encounter worthy specimens.