I just checked Eclipse: Green circle with a white, right-pointing triangle. Then I checked Netbeans: Green right-pointing triangle. Both of these are unmistakable icons for 'play'. Edit: I even googled for screenshots of Visual Studio...green right-facing triangle.

http://en.wikipedia.org/wiki/File:Vs2010rtm.png

Could there be a more universal idiom in the world of IDEs?