PhoneBoy is considered to be one of *the* authorities on all things Check Point, and has a not half-bad forum. He's written the one book that several people referred me to when I had initial questions about VPN-1... link to ISBN 0321180615

I can't say it's the best because it's the only one I've read, but it was pretty decent. Also, it's available via the O'Reilly Network Safari Bookshelf