Flash can be used in many great ways. One example is making music online using visuals.

Below are some pretty inspiring examples.

if piano is your thing check out Pianola

if beats are your thing check out this simple beat layering by Project Two

if glitches and cuts is your thing check out Glitchscape

if simple chords and rain dew drops sounds enticing check out this from Lullatone

you can even make music using our planets in the solar system with Solarbeat

and for you visual/aural pleasure check out this form of music making using movies cut/clipped/pasted using instruments like the pioneer dvj-1000. This is by a artist called Pogo (a video disc jockey) made with mixers similar to cd turntables but these are mixed with dvds. The music is not bad but its the way that its put together which is great.

There are a lot of  other sites as well to consider but these are the ones that sparked my interest.

If you know any sites similar to the ones above please feel free to share.