Some online timers designed for classroom use include the Dynamite Timer, the Rocket Timer and the Bomb Timer available at Online-Stopwatch.com. Once time expires on these timers, the dynamite and bombs explode and the rocket launches.
These timers all feature a cartoon-like drawing of an object that the teacher can render to full-screen or download through a projector. These and other humorous online classroom timers are available for free on the Online-Stopwatch.com site. This site also features egg timer/hourglass and metronome timers. Teachbyte.com is another site that features online classroom timers. A few of its timers include an online stopwatch, an egg timer and an iPad timer.