A nice site for basics on Digital Logic Design

http://www.allaboutcircuits.com/, Look up Volume IV - Digital

Summary of topics covered...

Chapter 1: NUMERATION SYSTEMS
Chapter 2: BINARY ARITHMETIC
Chapter 3: LOGIC GATES
Chapter 4: SWITCHES
Chapter 5: ELECTROMECHANICAL RELAYS
Chapter 6: LADDER LOGIC
Chapter 7: BOOLEAN ALGEBRA
Chapter 8: KARNAUGH MAPPING
Chapter 9: COMBINATIONAL LOGIC FUNCTIONS
Chapter 10: MULTIVIBRATORS
Chapter 11: COUNTERS
Chapter 12: SHIFT REGISTERS
Chapter 13: DIGITAL-ANALOG CONVERSION
Chapter 14: DIGITAL COMMUNICATION
Chapter 15: DIGITAL STORAGE (MEMORY)
Chapter 16: PRINCIPLES OF DIGITAL COMPUTING