Jeff Hwang's book is considered excellent.
Amazon.com: Pot-Limit Omaha Poker: Jeff Hwang: Books
It's great for beginning - intermediate, alhough I haven't found too much in there that I didn't know intuitively. But seeing the explanation of exactly why certain hands work hammers it home. Even though the title is Omaha PL, there's a huge section on H/L, both limit & PL. Definitely worth a read. Not sure of any other book out there that compares. I've read there was a small section in Brunson's 'Supersystems' that is good, but haven't read it.