First song I heard was Wonderwall, and I totally fell in love with it. It's still one of my favourite Oasis songs, and it scores pretty high on my overall favourite songs list too.
They also have a LOT of other good songs. Lyla, Songbird, Cast No Shadow, The Importance of Being Idle, The Masterplan, Shakermaker, Live Forever and Some Might Say are only some of them. I don't understand the haters, Noel Gallagher is a flippin' genius, and Liam's vocals are like the icing on the cake. SO much better than most of the pop music we hear today (*ahem* One Direction *cough* Rihanna *ahem* Skrillex).