Great site for quickly assessing students - can see results in real time. Can input class lists but don't have to. Each category can be easy to hard by selecting different levels. You can use what is already there or make your own. Try it out - it's free!
Tara- thanks for the post - wondering what your thoughts regarding appropriate level such as: geometry, algebra 1, algebra 2 or perhaps all the above. See if you can edit this listing and tag it with those levels that way teachers can search by their subject area and more easily find sites suitable to their class. thanks again for the great post.
Here is a more friendly version of Wolfram Alpha, essentially the google of math. Students can get step by step instructions on problem solving... this could act as an at home tutor. It is a sign up site, but it looks like this is free for teachers...not sure if there is a cost for students.