Bill Bryson's A Short History of Nearly Everything. Love everything he does but this one is particularly good.
Mary Roach - Particularly "Stiffs". The only nonfiction book about cadavers that will make you laugh out loud? Is that inappropriate? ...sigh....
Also, if you are all environmentally minded "The World Without Us" by Arthur Weisman (I think). Not as good as Bryson's (Bryson is quite humorous) but an interesting concept. National Geographic did a great documentary similar to this which was quite good.
ETA Just noticed you already know about the Bill Bryson. Sorry can't help you out with drm free.