Any good recommendations for books (or other sources) on pagan traditions and beliefs?

I'd br interested in what you'd consider a good book (or other sources) on various pagan beliefs and traditions that you would recommend.

I'm personally interested in European pagan traditions - be it Norse, Celtic, Germanic, Slavic (bonus points for Slavic!) - but would love to leave the topic open to others as well, just to make it interesting for people with different intrests.