If you are using these files to plan and write essays then Scrivener may be suitable. I’ve not used it but I downloaded it today hoping I can use it to store my work notes.

I don’t think this is really what your looking for, but I’ve been using both Schoolhouse (http://www.loganscollins.com/schoolhouse/) and Taskpaper(http://hogbaysoftware.com/). I use schoolhouse and put all my assignments in, and you can attach files to an assignment(e.g. like a prompt for an essay), and then I use Taskpaper as a todo list and tag each item with its class and due date.

I’ll second Scrivener for getting your writing projects under control. Its full screen mode is perfect for blocking out all distractions and it was designed by someone who is a writer himself.

For word-processing and formatting I would recommend NisusWriter Pro. It may be more than you would need for high school, but as you get into writing larger papers, nothing beats its killer search/find/replace features, and formatting is a lot more intuitive than Word.

Bookends X is also a wonderful, and very mac-savvy program for managing all of your books and for automatically formatting your footnotes and bibliographies.

I’m also partial to my own programs — Ready-Set-Do! — a file-oriented approach to getting things done on the mac. And Speak It On My iPod — that converts text into audio you can listen to on your iPod or iPhone.

If you try Ready-Set-Do!, you’ll want to read the “How to Use RSD” file so you can see how it can help you plan your projects. If you assign a due date to a project — say, a paper due at the end of the semester — it automatically calculates the deadlines for all of the sub-tasks you’ll need to get done to finish it on time; and the tasks turn Yellow -> Orange-> Red as the deadline for each one approaches. I always wanted a program that would not only tell me when something was due but would also tell me when I needed to get everything else done in order to get the entire project done on time. So I wrote a program that finally delivers that for me. It takes some getting used to, but it’s a pretty cool setup.

Hope that helps.