This is the code I am working with:
http://jsfiddle.net/4XBtQ/1/
You can see that the right sidebar is sitting at the bottom of the left column. There seems to be a lot of different ways of positioning the sidebar on the right, but what is the correct way?
There is no “correct way”, it all depends on how you want it to behave.
If you float both main and right to the left (float:left), the results will be like you describe.
You could also use absolute positioning on the right column, if you want it to avoid “floating down below main” if the contents would grow too big.