Hi Buddy!
Well, you know this area is really big. You'd better explain what subject you are interested in. Please tell me about it.
But I know some good basic books about "Microwave Engineering" :
1) Microwave Engineering 3rd Edition by David Pozar (a new book with new subjects)
2) Foundations For Microwave Engineering by Collin (an old book but with descriptive bases)
More specific, if you want to learn about "Microwave Transmition Lines", I know two old but useful books too:
1) Microstrip Lines and Slotlines by K.C. Gupta, Rames Garg and I.J. Bahl
2) Foundations for Microstrip Circuits Design
I know others about different subjects; if you are interested in any othe one please tell me.
By the way I have some PDF's about "Microwave Engineering", I can give you them if you would like.
Thanks!