Roland TB-303 Emu in Flash!
… Ok, a bit of exaggeration here but it comes pretty close! In case you missed it, Andre Michelle has written a RealTime Synth with ActionScript 3.0 that immitates an analogue synth not unlike the famous 303. The Userinterface is slick and the knobs are turning linear when dragged with the mouse. The sound is very good for that it is calculated! Try playing around with the Filter, Cutoff and ADSR curves and you will see (hear) that it sounds pretty much like a real synth. Heads up to Andre for being such an Innovator!