Socks and underwear are all well and good, but if you want to give your favorite geek a gift that keeps on giving, zip down to the hardware store and pick up a couple of sets of rechargable AA and AAA batteries and a recharger.
Sure, batteries are anything but glitzy, but your technically-adept pal will thank you when he or she needs to put some power back into an Apple Wireless Keyboard and Mouse, a digital camera, or the portable music player used when the iPod is recharging.