A collaborative and ongoing project started on Google+, the Web Tools Spreadsheet seeks to identify free web tools that can help teachers improve instruction. You can view it here: http://ericstockmeyer.blogspot.com/p/width860-height700-frameborder0.html
Know of a web tool not on the list. Submit it here: http://ericstockmeyer.blogspot.com/p/web20-submission-form.html