And speaking of Ultimate, Nyaa.se, of course. It is particularly useful when searching for lossless versions of the bonus CDs that accompany DVDs/BDs. Some release groups will release the ape+cue of the bonus CD along with the "raw" video files (as each volume is released and/or as a batch). The already mentioned groups like Nipponsei, ASL, and animeost.info also post torrents of their releases there, too.
hikarinoakariost.info (I think just MP3; updated frequently)
blog.shinnoden.net (Shinnoden, also goes by Shin-S. Mainly MP3, but occasionally FLAC, too).
Other resources, not necessarily places/sources where you can obtain music from, vgmdb.net and cdjapan.co.jp can help you obtain track lists, release dates, album catalog numbers, etc.