I have found the best spy gadgets reviews resource – the Spy Review blog which is full of great spy gadgets and it is updated regularly.
You will find a lot of cool gadgets on The Spy Gadget Blog like: Tactical Night Vision, Whoâ€™s at the door? – Covert Peephole Camera, Spy Lazer Tripwire kits and Wireless Color Camera hidden in Cigarette Pack.
My favorite is Making your own lock picks – Using a PC, a tutorial about how to pick a lock with your PC.
You will also find on Spy Review security related books, surveillance suppliers and useful circuit diagrams.