Kukuklock is a really cute online alarm clock – great to use as a timer for so many things in the classroom.
Classtools.net is a great site with some really cool things to use in the classroom like these
Random Name Picker – great for unbiased selection of kids or for looking at probability
Countdown Timer – not only does it have a myriad of uses in the classroom but you can choose the alarm you want from a huge variety of really fun sounds
Block Posters.com is a great site. It takes your images and turn them into huge pictures that you can print out in sections and join together