Hunkin's Experiments offers over 200 science experiments freely available in comic strip form. The experiments are organized in 18 different categories, covering a wide range from simple trickery to more technical experiments. The author, Tim Hunkin, is a trained engineer turned cartoonist, and also responsible for TV series/site The Secret Life of Machines (worth a look).
Some of my favorites below, click through to Hunkin's Experiments for more.
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