I think though it's probably worth pointing out (someone normally does when these threads periodically pop up) that the songs themselves don't really matter as much as your knowledge of them.
Of course it helps to have something that sounds good and is balanced and well recorded etc, and some of the suggestions on here are great sounding tracks.
But at the end of the day the track itself isn't so important, the important part is that you should know the track inside out and back to front, and should know exactly what it should sound like when played through a good sound system.
That way, if it doesn't sound the way you expect it to then you hear it instantly and can start to troubleshoot the problems.
So the best idea is to pick a few well recorded tracks that you know well, even if they're different from other peoples suggestions, and work from them. Play them in all different sound systems and get to know if this part sounds a bit honky or if this part sounds a bit boxy etc what that actually means in terms of what frequencies may need some work, or what the problem areas may be based on what you're hearing.