Though I don't have any real favourites, there are certain bands I keep going back to again and again.:
Buffalo: A little known Australian band from the 70s. They toured Australia with Black Sabbath at one point, if I'm not mistaken. Commercial radio essentially blacklisted the band, and by the time public radio stations came along in Australia, it was too late. The spark had dissolved amongst lineup changes and a change of direction. Shame they never got big. I'd highly recommend the Only Want You For Your Body album to any fan of 70s rock or early heavy metal. Don't worry, not all the songs are about sex. Here's the opener.
Van Der Graaf Generator: VDGG take lush, pleasing harmonies, outstanding organ work, tight grooves, intelligent, thoughtful lyrics, remarkable vocals, psychedelic sax work, memorable, catchy melodies, jazz influenced drumming, and, at their live shows, a great degree of weight... where was I? VDGG take these elements and combine them into progressive music that is not at all flowery or ostentatious. Like many prog groups, VDGG isn't always simple thing to get into, particularly to an ear that isn't familiar with prog. I listened through the Still Life album three times before it really hit me.
Gorguts: Not only do they play death metal, but they're also quite avant-garde. Their release Obscura is one of my favourite DM records, next to Carcass' Necroticisim - Descanting the Insalubrious, Edge of Sanity's The Spectral Sorrows, and every record Death put out. Obscura is a truly original offering. It's technical, but not wanky. Crunchy, but not entirely atonal. Unconventional, but not pretentious. Natuarally, it's outside of your average comfort zone.
Charles Mingus: I once had a music teacher call Mingus the Shostakovich of jazz. The man was an amazing composer. He wrote my favourite jazz album of all time, The Black Saint And The Sinner Lady. His music is emotionally dynamic. It can lift your hear or crush it, it can put a sparkle or a tear in your eye. It's also quite enjoyable, too. Some people say he plays the bass a bit too abrasively. but screw them, they haven't been hit up in their souls!
Not to be confused with Art Blakey's Moanin'.