Circuit and board designIf you want to design your own circuits, pcb's or similar you're probably gonna need a program to help you. Here's a few links to programs that can help you.
SoftwareDiylc - "Do It Your Self Layout Creator", Layout pcb, stripboards, perfboards or just schematics.
LTSpice - Simulate circuits
Making PCBsTrasfer patterns using glossy photo paper
Super fast etching using minimum etchant - This page looks at first glance as something where you'll find more ads than information but it really is a valuable resource.
Edinburg etch - A little more technical (chemistral even) information on how to spice up your etches (pun almost intended).