Soft Cell - Tainted Love (one of the most-played songs on the radio, at one time, anyway) is apparently about MDMA (as reported in Sheryl Garratt's "Adventures in Wonderland").
I can think of a lot of hardcore tracks about E.
older ones:
Altern8 - Activ8 ('top ones, nice ones, get sorted')
Moby - Next is the E (although he doesn't do drugs...)
3 Thieves and a Liar - Soothe Like a Pill (only because it has 'pill' in it)
middle-school hardcore:
Force and Styles - Follow Me ('follow me, and i'll let you taste my ecstasy')
Hixxy - Wanting to Get High
actually, that's all that comes to mind right now. a lot of hardcore tracks mention ecstasy, but i can't think of many more right now. it's a nice word, because a lot rhymes with it (destiny, fantasy, galaxy..) most references are about love making someone being in ecstasy or something, rather than actually about drugs, but when you drop that word in hardcore the meaning is pretty obvious.