Electrical Engineering/Computer Science(hardware):

Modern control systems (9th ed.) by Dorf and Bishop
Computer organization and design: The hardware/software interface (3rd ed.) by Patterson and Hennessy
CMOS VLSI design: A circuits and systems perspective (3rd ed.) by Weste and Harris
Microelectronic circuits (4th ed.) by Sedra and Smith
Analysis and design of digital integrated circuits: In deep submicron technology (3rd ed.) by Hodges, Jackson and Saleh
Computer systems design and architecture by Heuring and Jordan
Modern VLSI design: A system approach by Wolf
Signals and systems: Using the web and Matlab (2nd edi.) by Kamen and Heck
Contemporary logic design by Katz
Basic engineering circuit analysis (6th edi.) by Irwin and Wu
Adaptive system identification and signal processing algorithms by Kalouptsidis and Theodoridis
Classical data structures in C++ by Budd

Economics:

Mathematical methods for economics by Klein
Basic econometrics by Gujarati
Essentials of engineering economics by Riggs
Fundamental methods of mathematical economics (3rd ed.) by Chiang

Math:

Introductory Combinatorics (2nd edi.) by Bogart
Advanced engineering mathematics by Zill and Cullen