Not too many books that focus strictly on limit Omaha - only two I can think of is the one by Mike Caro and Mike Cappelletti and Mike Caro called Mastering Holdem and Omaha and Championship Omaha which covers all the forms including limit
Ray Zee's "High-low-split poker for advanced players" is likely the best book out there. Probably the only book worth a read, in fact.
+1
I think that one of the Super System books may have a section on Omaha 8 too, but if you read High-Low Split Poker for Advanced Players, you won't gain anything from that. HLSPAP is definitely the way to go.
Don't skimp on the reading, either. The book is in two sections, one for stud 8 and the other for Omaha 8. Definitely read the whole thing.
