For about the past month or so I've been eyeballing PSK31 for ham radio. It's one of the newest protocols for digital transmissions for ham radio. PSK31 allows radio operators to send text messages back and forth rather than morse code (CW) or speech (phone). It's like chatting without a network connection.
Granted, many of the regular readers on neodux aren't ham operators, but it is a very interesting aspect of radio that begins to border line on hackable projects. In the event you ever wanted to start with PSK31, here's a primer. There are plenty of freeware programs to allow you to decode PSK31. All you need is an HF receiver, a verymodest computer and an 1/8"-to-1/8" stereo cable to hook the radio up to the computer. Install one of the PSK31 programs and you'll see text streaming in from current hams conversing over a whole array of topics. It's amazing that the computer is able to pull intelligable data from amid a whole field of static. I was able to read text from a signal I could barely hear, but could only see on the "waterfall" display. Another cool aspect is the lower power requirements of PSK31. 100W is overkill to work the world! To transmit you might need a slightly more advanced setup than a single wire, but nothing you can't build cheaply or conveniently purchase from plenty of vendors online.
While at the Belton Hamfest, I saw a DB9 model for Yaesu radios, I would've bought it if it would've worked for my Icom 706mkIIg.
update: I've now ordered a USB interface directly from Saratoga Amateur Radio which should be in shortly, and I'll post more on it after I've had time to break it in.
Also for the curious, here are a couple more links about PSK31.
If you really want to know, here is the PSK31 author's primer on how it works.