CircuitryCesigns PCB articles A collection of application notes on PCB topics by various vendors http://www.circuitrydesigns.com/category/PCB-Design.htm
Understanding & Interpreting standard logic datasheets A good tutorial on understanding the various terminology, and how to interpret the information given in digital datasheets, relevant to your design project requirements http://focus.ti.com/lit/an/szza036b/szza036b.pdf