Something that I have found useful with lots of students (although at the moment primarily only GCSE) is the ability to give them multiple choice tests using the quiztest system which is a nice OSS script that works with flat files to produce tests you can give students. I'll put more material up as time goes on. The software that I use for this is the quiztest system written in pearl.
I'm aiming to produce a system for sharing/distributing tests that I have made over time so that other people can find them useful. I have more recently seen a demonstration of moodle which I think will/has superseded this.