Alex
I've seen it many times whilst flying in one of HM pointy jets and have seen it most recently in an A321 on climbout from Birmingham. We were both trying to recognize star constellations when the St Elmo's fire started. We instinctively 'leapt' backwards and I quickly got out my digital camera. Unfortunately, although it was the most spectacular occurrence I'd ever seen, by the time I got the camera running, all I caught were the last couple of flashes. If you PM me with your email address I could send you the file if you're interested.
By the way, we weren't in cloud at the time and there were no storms nearby.
Better yet, I've just a quick search with Google and there's a very good image of St Elmo's Fire as it appears on aircraft windshields at:
http://en.wikipedia.org/wiki/St_Elmos_Fire