[punter11235]

PLO chapter in "potlimit and nolimit poker" by Ciaffone & Reuben is very good.
"How good is your potlimit omaha" by Reuben is not good in my humble opinion.
I heard that "Omaha Poker" by Ciaffone is good but I dont know anything about it as I dont have it (its out of print now).
Dont buy anything by McEvoy. Its not worth it.
The best thing about PLO ive ever read is Steve Badger article abou PLO/8 (yes, its about PLO/8 but general concepts apply to PLO as well) you can find it on his webpage.
Also search for poster "robbo" ( or sth like that) he has very nice webpage about PLO with some discussion about hands. Unfortunately I dont remember exact poster's name and web address so it may take some time to find it.

Hope that helps.