A concrete description of the product being developed. Bonus points if I can actually get a demo copy of it to play around with before applying. I'm amazed at the number of job listings filled with a lot of verbose abstract language that never gets down to the meat of what it is they'll expect you to be making.

Other than that, any mention of good coding practices (automated testing, continuous integration) or technologies that show the company is keeping up in the field and not getting too bogged down in a lot of legacy code.