What is Your Favorite Linux Gadget?

With the gadget-focused December issue of Linux Journal hitting newsstands any day now, I thought it might be fun to know what YOU think are the coolest gadgets out there. There are many devices mentioned throughout the December issue (check it out to see what's under the hood and how to hack some of them). Tell us which one appeals to you, and feel free to expand in the comments, or let us know some cool ones we may have missed.