2.4GHz parabolic mesh dishes from Chinese cookware scoops & a USB WiFi adaptor! Called "WIFRY","WOKFI" or "WOKTENNA" (12"= 300mm diam) shows 12-15dB gain (enough for a LOS range extension to 3-5km)
Weekend Project Podcast: Make simple radios to listen too. These were made with materials that they could get their hands on and were small enough to carry around in a big pocket.
four-channel GPS receiver using a repurposed FPGA board from a previous frequency synthesizer project. Connected to a PC running a console app, the receiver is capable of tracking four satellites simultaneously, which is good enough to capture lat, long, and altitude.
basically the Flash Nap project with a few extra features and some work. It's also a minimal version of "Light/Sound" hypnosis machines that cost hundreds of dollars, but if you have parts, this one will cost just a couple of bucks. NO PROGRAMMING REQUIRE
Nice little guide to building an IR transceiver - uses the USB port for stable 5V, but includes a link in the comments to a decent circuit diagram that uses a voltage regulator and therefore doesn't need the USB port for power.
A remote control car that can be driven over the internet or with a laptop wirelessly from up to 500m away. It has a live-feed network camera so that it can be driven without line of sight and a horn so that you can honk at people.