You could use the techniques you saw in awesome CSS3 or WebGL demo.
You may get inspired by these demos to do something different.
Even simple looking at stuff (if it's not awesome enough for you to check out at how it's done, or you're not a programmer) at least refines your understanding of possibilities of different technologies, that kind of knowledge we use often without noticing it.
Hell, a post with playing paint.exe as audio data might give an idea for a killer 8bit chiptune dubstep track!
They say that even watching TV might be useful, depending on how you're doing it. (Can't remember the source, ironically.) So, we shouldn't be quick at labeling things useless.
After all, you probably have an ulterior motive in making something useful: that's pretty much the definition of "useful". But something complicated and useless? That's just cool.