Someone recommended awhile back a website where you...
1. Scanned your books (hand scanners are on Amazon for ~20),
2. Boxed them up,
3. Sent them to the company (they paid the shipping)
4. Received a check.
I cannot for the life of me remember the name of this place. Hold on...
Here we go:
http://www.cash4books.net/faq.php
EDIT: Ah, crumbs, they are US-only. Maybe there's a UK version though?