The Joe M and Ed B books are great.
Often underrated is the Joe M book "Side Mount Techniques". It's something like 100 submissions from the side, all chained into flows. If you're ever in the market for that topic, it's a great resource.
I've always liked the Renzo / Royler book as a good starting reference.
I also like a number of the Judo Masterclass books. In particular, the ones on Grips, Russian Judo, Pick-ups, and Osaekomi are highly relevant to my BJJ.
The best takedown book I ever found is "Wrestling: The Making of a Champion, Vol 1: Takedows" by Bobby Douglas. EXCELLENT wrestling takedowns, and often it can be found very inexpensively.
And if one is venturing beyond strictly "BJJ" books, then Jigoro Kano's Kodokan Judo is not to be missed. There is also a lot of great theory in "Aikido and the Dynamic Sphere".
And for hilarity, Gene LeBell's Encyclopedia of Finshing Holds. Wowsers.