My Favorite...

I love to find small, eclectic thrift stores and antique shops to wander and meander in. Exploring hidden nooks and discovering forgotten or misplaced treasures is extremely thrilling.
I try to avoid the Crossroads/Buffalo Exchange type of atmosphere, which I find much less intimate.
One of my very favorite places to find vintage/cute/used clothing is The Painted Bird, located at 1201A Guerrero St (24th and Guerrero) in San Francisco. Only about two blocks up from Valencia (best wandering around area ever), it is extremely small and extremely homey (through the curtains of one of the dressing rooms you can actually see into the kitchen of the area the owner lives in).
They buy/sell/trade clothing just like any other consignment shop but it's much smaller than the more known ones and therefore has higher quality. The cutest (and most friendly!) girls I've ever seen work there. I'm always admiring their cool outfits out of the corner of my eye while I quietly look through the racks of vintage jeans and sweaters.
It's seriously the most awesome place ever, and it's small size does not indicate the amount of time you can spend inside (I've waisted many a day). Quality over quantity is definitely how they do business.
There's also a really cute coffee shop across the street with health foods...