I like to use the term "famously good". Unfortunately, that sets the bar extremely high. Not as high as it seems, though, since I mean, "famous in our segment of the market or for working with our preferred technologies". e.g. They've written one or more books on the topic, they headed up a popular FOSS project in the area or in the language, they wrote the definitive implementation of a really interesting concept, they have code in our language implementation (where language for us is Perl and JavaScript--so patches in the Firefox JavaScript engine or Perl 5 or Perl 6 are interesting indicators), etc. We'd even consider blogging to be a "famous" trait...though we'd want to see some code.
So, by that definition there are at least 50 people on HN that I'd hire without hesitation. And by that definition, I've worked with and for at least a couple dozen famously good people in my ten years in the industry (and the longer I think about it, the longer the list gets).
Interestingly, when I read "Rock Star Developer", I think, "Will work your ass off, get no equity, and get salary on par with the industry average." And when I think, "famously good", I think, "Will expect salary that is commensurate with output, will expect to work on interesting projects, and has his/her pick of jobs." And yet, the latter is who I want to hire, because I know the difference it makes in quality and productivity. If I can hire a famously good hacker for about 1.5 times the industry average, I'd consider it a good deal.
But I use the term because I know what it means...I'm not sure if it'd be meaningful to folks reading our job ads. So I'd probably be more explicit about what we're looking for.