My calculus II course requires students purchase a code (I paid $30.76, Indiana state tax included) to enable a term's worth of access to WebAccess. The site has many exercises for the chapters being covered in my course. Each exercise has links to the textbook, Stewart's Calculus, 7th edition; the entire textbook is readable through the site, although it is probably awkward to try to use it in lieu of purchasing the textbook outright.
So far I have yet to use the Help buttons, but my classmates have been dismissive of them.
It is early days for my use of WebAssign, but it looks like it will be a good method for reinforcing the content. Regardless, I will work many of the odd exercises in the textbook for additional practice.