principles of brewing science by george fix is a good'un, the hough, briggs, stevens and young series, malting and brewing science are supposed to be good but ive always baulked over the price
'Brewing Microbiology' by Campbell and Priest (I think those are the authors, not at home right now) is an excellent book. Goes into real detail of the whole process from the grain growing to the finished product.
+1 on "Yeast". I'm a microbiologist too and am currently reading it. It's nothing you haven't ever learned before, but it's wonderful to see it all laid out on how it ties into the whole brewing process.