Deadpool Classic, Vol. 2: Joe Kelly, Ed McGuinness, Kevin Lau, Pete Woods, Shannon Denton, John Fang, Aaron Lopresti, Bernard Chang: 9780785137313: Amazon.com: Books
I say start with Vol. 2 because Vol. 1 is mostly the Rob Leifeld stuff before he was funny. Unfortunately, the very first issue of Joe Kelly's run is in Vol. 1 (because otherwise everyone would skip it, probably), but you'll be fine starting with Vol. 2. I want to warn you that this isn't Watchmen. The book doesn't really hit it's stride until later, but from here you get some good fun and a couple laughs. It's a good starting point.
I want to say that the newly released Gail Simone book would be a better starting point, but I need to re-read it first. Hopefully, my shop has the copy I order when i go to pick my books up this week and I can let you know.