Places to acquire old books

(from a thread I started on book-arts yahoo group...

Hi. I thought I'd start a thread to address the question of where to get old
books at a cheap price. Anyone with other ideas, please chime in.
1. Friends of the Library Booksales are awesome. Usually hardcovers are no more
than $1... and the last day might be $1 a bag.
2. Thrift stores (NOT "antique" stores, NOT flea markets) and if you find the
"name brand" stores have gotten too expensive (Goodwill, Salvation Army, St.
Vinny's), google for more obscure thrift stores in your area where they haven't
upscaled their prices yet. (Hospice, Hospital, Senior Center, Church, etc). eg.
I visit a senior center thrift store where hardcovers at 50 cents...plus they
put some of the books out front in a free pile.
3. Yard sales, esp. at then end of the sale when sometimes they give things
away.
4. My local library has a bookshelf up front with free magazine and free books.
5. I don't EXPECT to find the perfect thing on a given Saturday search. It's the
kind of thing that over time, you accumulate.
6. Freecycle and craigslist free stuff...
Any other ideas?
Anita