Technically I found out about Dream before any other Jpop artist, and that was in...*thinks hard* 2000...? I'm pretty sure. I loved them, but couldn't find anything else by them. That was back when I was into para para.

Then I found out about Ayu through some guy in my Japanese class back in...2002? 2003? Around then.
Right now my favorite Jpop artists are:
1. Ayu
2. Ai Otsuka
3. Koda Kumi
4. Namie Amuro
5. Utada Hikaru
6. Arashi
Those are about the only Jpop artists that I listen to on an everyday basis. I do spice it up a bit here and there, but I have yet to find a new artist that I truly like. I really like Alan, but her music is too soothing to listen to all the time when you're feeling any mood.