There is a myriad of websites available online which can give you all sorts of learning tools. My personal favorite is Atomic Learning.com, which teaches you how to do integrative technology. For worksheets, and other activities there are also plenty: Apples4theteacher.com; superteacherworksheets.com; tlsbooks.com, and there also is TeacherTube.com. TeacherTube is very similar to YouTube, but teachers basically are the ones who upload their material (including yours truly).
For powerpoint presentations you should go to slideshare.com, or box.net.
All those sites are free of charge. In any case, go to google and type in "free teaching sites" and you will find way more than you will ever think. So, try it out and let us know what u think.