We (myself and a fellow zebra with the league) have designed a great big LED scoreboard that you can build for around $200. It's not software, it's a big thing you can carry around and kick if it pisses you off.
The plans are free, the firmware for the AVR microcontroller is free (source code included, MIT license), and I will personally help you put it together as best I can over the Internet. A skater in California has just finished building a third one of these, so I finally feel confident enough to announce it to a broader audience.
If you play outdoors, this is way cheaper (and way more labor intense) than finding a sufficiently bright projector. I want to make sure I communicate that this is a lot of work: it's not something you can knock off in a weekend. Plan for it to take at least a month of weekends.
Stop by
https://code.google.com/p/derby-scoreboard/ for plans, wiring diagrams, code, and everything else you need to get started. You should probably email me too (neale@woozle.org).
