I heard X-Press II - Music X-Press the other day, and it reminded me what an great tune it is. One of those songs that is near perfection for what the tune needs to be/do.
From the "old school", my faves isSashie Tomie/Frankie Knuckles/Robert Owens Tears, closely followed by Joe Smooth - Promised Land.
The thing is, I'm not really that old enough to have had life changing experiences to these tunes. So my "classics" come a bit closer to now.
I would say Bob Sinclar - I feel For You changed my life in the same way Tears changed a generations.
I also hold MaW - To be in Love, Bangalter and Falcon - Together, Cleptomaniacs - All I do, Jazzy M - Jazzin the way as my favourite "classics"