I'll recommend Ai Am Best too

, that album got me into Ai-chan's music. I'll also recommend Utada's latest compilation album, it dosn't come with a DVD, but it has a second cd with 5 new songs in it. B'z's "B'z The Best ULTRA Pleasure" is great too if you want to try j-rock, no dvd for this one as well, but it has a LOT of songs.