In a bank or the shelf of the ATM.
Not near any store selling new books - they really get aggravated there :o)
I've tried park benches, on top of mailboxes, benches at bus stops. I used to leave them in cafes, but you might have to lurk & watch to make sure the staff don't throw them out.
All over West Edmonton Mall, which is near here - most of my catches were other BookCrossers hunting from my release notes.
I left a mystery novel with a wedding theme outside a bridal shop. Novel set in a bakery outside a bakery; you get the idea. Not sure if the catch rate was improved but it was fun for me.
Try anything at least once - you never know!