A slideshow of the "30 Best Web 2.0 Tools" that contains many popular tools. Most are free (although a few have costs involved) and chances are there may be one or two that are new to you. "Each slide...contains the name, description, link and screenshot of what each tool looks like and does."
Have fun exploring and bringing a new tool into your classroom.
Via Beth Dichter, Timo Ilomäki, Gust MEES