Text is really one of the best I think.
And you've got a good file heirarchy, that helps a lot too. Extremely portable and searchable straight from the file manager tools. Assuming you're using windows you can do file name searches and file content searches from windows Explorer or use the Google Desktop Search. Vista offers good searches right from the Start Menu.
If you want to add images, I'd recommend learning some basic HTML/XML. Your text files can be marked up fairly simply and your file hierarchy is already good for these mark up languages. A bit later, I'll point you to a wiki style tool as well you might like for this purpose.
Still very searchable with basic free tools in the operating system and compatible with email, cell phones, PDAs and so forth for recipe portability.
Another handy tool for such recipe archives is HTTrack.
HTTrack Website Copier - Offline Browser This tool copies existing websites for your local offline browsing. It doesn't work with all websites. Some database/script driven websites are incompatible but there are a lot of them that you can save for your own use. There are ways for you to use log-in accounts with it as well for whacking private sites. Good also for backing up a web site of your own.
If you want more powerful searches, you can set up a wiki on your personal computer. Again, your basic text files are a good start for this project. You'll need a software engine to do the indexing searching and so on, but there are some free ones out there. Here's an article for setting one up on your PC
Organize Your Life With A Wiki | Maximum PC
Phil