Just published EasyDex Crystal, a free web app to help you complete your Pokedex in Pokemon Crystal. Features include:
- Listing of Pokemon showing the easiest way to obtain them
- Filters such as All, Solo, Trade, Grass, Cave, Fishing, etc
- Ticking off Pokemon you've caught and tracking your progress
- Get your Pokedex rated by Professor Oak
- Get a link which you can paste on forums, websites etc. Others can click that link and see which Pokemon you've caught
The best way to find out about EasyDex Crystal is just to use it! It's written in HTML5 so there's no download. There's a nice welcome screen which explains its features.