As any good Time Lord knows, nothing impresses the female companions like tightening a few bolts with sound waves. That's why the Doctor never leaves the TARDIS without his sonic screwdriver, a nice tool to have around when you're facing the evil of the cosmos on a daily basis. This replica of the one in the TV series won't get you out of any scrapes with the Daleks (or tighten any bolts for that matter), but it'll come in really handy if you need to write anything down.
Too conventional for you spacetime veterans? Don't worry — just like the end of any decent episode, there's a twist! In addition to a regular pen, the Dr. Who Sonic Screwdriver has a second tip that writes in invisible UV ink. To see the secret messages, just shine the screwdriver's UV light (a.k.a. black light) over the note. It also makes authentic sounds from the TV show, and the pad shown is included. For $15, the payoff in fun is well worth it… as long as you're careful not to reverse the polarity of the neutron flow.