R136a lies in a neighboring galaxy, and is the new title holder of most massive star.  That's right, even bigger than Britney, Lance, and Kobe put together.  Here's a decent write-up .  What I REALLY love, though, is how when this kind of stuff gets written up, scientists are always astonished, perplexed, or amazed.  I mean, come on.  Really?  Anyway, it's not in the article, but I LOVE this size comparison, so here ya go.