Because I like to tinker and because my wife is out of town, I just bought and installed a Matrix Orbital MX610 LED display for my computer. The MX610 is a configurable 2-line display that shows you exactly nothing that you can't otherwise show on your PC's monitor. But man, is it cool. I've got mine cycling through real-world data like the time, weather, and stock quotes, as well as system information like my CPU's temperature and network bandwidth.
The coolest thing about this MX610 is the third-party software that comes with it: LCDC. It lets you configure the display to show just what you want, and how. It can also respond to events on your PC. For example, mine automatically flips to the CPU temperature display when it gets hot; it would be easy to do something similar with stock quotes. There are several free plug-ins available to display things that aren't bundled with the system. For example, there's one to display Caller ID information (assuming you have a modem that can capture it).
More advanced users can use the MX610 and LCDC to control system fans, and to turn on other devices (mostly lights, but also relays) when events occur -- for example, when new email comes in.
The gizmo is designed to mount in a 5.25" drive bay in your PC, but I put mine in an external enclosure since my system is on the floor and I didn’t want to have to crane my next to see it. I'm actually using it as a riser for one of my monitors.
Next up on my tinker list: I want this thing to display RSS feeds. A plugin for this comes with LCDC, and I look forward to setting it up. I just need to take a dinner break first.