A small antenna to boost the signal of a laptop wireless card, that can be stuck to the back of the laptop screen.
The W1GHZ Online Microwave Antenna Book
This page details the construction of a biquad antenna. The biquad antenna is easy to build, and provides a reliable 11dBi gain, with a fairly wide beamwidth.
This website details the design and construction Wave Bubble: a self-tuning, wide-bandwidth portable RF jammer.