An alternative-history detective novel, set in a world where Israel lost the war in 1948, and a large Yiddish-speaking Jewish population settled in Sitka, Alaska instead. Really good stuff; it'd be a decent detective story even without the setting, but the sheer level of detail in the world -- most of it quite subtle -- elevates this to instant-recommendation level. I'll definitely be looking for more of Chabon's work. (Later: yep, his other books are good too.)
ISBN 0007150938. Search for this book on Wikipedia or isbn.nu.