I just finished reading Daryl Gregory's Pandemonium, a matter-of-fact heartbreaker about an alternate world in which demonic possession is a fact of life. I had the same reaction to it that I had when I first encountered Charles Petzold's The Annotated Turing: "Damn, I wish I'd written that." I don't think anyone's ever had that reaction to any book or software I've ever written (Beautiful Code doesn't count---I only edited it). I don't have anything on the go that's likely to either, at least not in the 416 days that remain in my contract with U of T.
So how about you? When's the last time you saw or heard or used something that you didn't just like, but wished that you could take credit for?