Ministry of Sound- the Annual 2003, specifically the first disk.
My dad played in the car and I thought "what the hell is this?" but at the same time it felt so deep and intense that I knew I had to have more. Especially Scooter with their weird nonsensical lyrics and catchy synths. I was only in 2nd or 3rd grade at the time and it was like hearing music for the first time.
There were other electronic music artists that I'd heard and liked before that, but not the same genre, and I'd still say this is the album that started it all.