Got a $50 Gift Cert to Amazon.com. What should I get?

Looking to get probably 2 more poker books. Here is what I have have read:

Super System 1 and 2
HoH 1 and 2
ToP
SSHE
Aces and Kings
One of a Kind
The Professor, Banker and Suidice King
The Making of a Poker Player
Caro's Book of Tells
WLLHE
The Psychology of Poker

I started out playing NL Holdem and got into Limit pretty hard about 8 months ago. Played that exclusively. Looking to move on to another game for a little while to expand my poker skills. Thinking about Omaha 8. What would be a good book for someone just learning Omaha 8? I was wanting to get 1 Omaha book and 1 general poker book. I really like the novel type entertainment reads but love the general poker strategy books (like ToP) too.

Thanks for the input.

Danny