Honestly, I would recommend both "B'z The Best ULTRA PLEASURE" and "'B'z The Best ULTRA Treasure"!
Their earlier stuff was pop, but it's kind of pop/rock now.
The DVD for "ULTRA Pleasure" contain best of live clips from their LIVE-GYMS (their equivalent of Ayu's ARENA TOURS) and "ULTRA Treasure" contains the concert "B'z Showcase 2007". (I'm such a fangirl!
) Utada Hikaru Singles Collection ~vol. 2~ is highly, highly recommended!!
She makes amazing music!!
YUI's SHORT STORIES is another I'd recommend.