Hacking sub $10 gadgets

Even the most frugal of us now have the opportunity to hack, with the increase in sub $10 gadgets. I wrote a few weeks ago about the TI MSP430 for $4.30. Here are a few projects to get you started with one.

Yesterday I was able to order an RTL2832U based R820T DVB-T for under $10 off ebay. Using rtlsdr you can use this as the cheapest software defined radio (SDR) I've ever heard of. Are there any other sub $10 gadgets you're aware of that are worth checking out?