He fired Zakk Wylde because he felt that Zakk's songwriting was beginning to make his songs sound like Black Label Society and Ozzy wasn't too happy about that. This prompted him to fire Zakk, albeit on friendly terms.
Ozzy's also said this is why he's never worked with Rick Rubin. Rubin wanted to make a heavier, Sabbathy album while Ozzy wants to get away from that. This was also part of the wedge between Ozzy and Sabbath. Ozzy just wanted to make straight up rock music while Sabbath were experimenting with jazz and strings. Hilariously enough, Rubin is the producer on Black Sabbath's 13 album (the first with Ozzy since 1978).
Dye Hard: Used to be, anyway. In the 70s his hair was his natural brown. In the 80s he dyed it blonde. Back to brown for the 90s, then when The Osbournes surfaced in 2002 he'd dyed it black with red streaks. It's brown as of 2010, but we'll have to wait and see if it stays that way.
Blizzard of Ozz and Diary of a Madman: The rhythmic section was composed by former Uriah Heep members Bob Daisley (bass) and Lee Kerslake (drums). Daisley also played in Bark at the Moon, The Ultimate Sin and No Rest For The Wicked.
Speak of the Devil and Tribute: Brad Gillis, from Night Ranger, had to fill Randy Rhoads' shoes, while Rudy Sarzo (bass, also Randy's former bandmate in Quiet Riot) and Tommy Aldridge formed the rhythmic section. Aldridge also played in Bark at the Moon.
No Rest For The Wicked: This album marks the debut of Zakk Wylde on guitars, while another former Uriah Heep bandmember, John Sinclair, plays keyboards.
The live EP Just Say Ozzy features Ozzy's former Black Sabbath bandmate Geezer Butler in bass.
No More Tears: The bassist who wrote the riff to the song "No More Tears" is Mike Inez, currently of Alice in Chains, and who also plays bass on Live & Loud. Also credited in the album is Lemmy.
Ozzmosis: Geezer Butler plays bass, while Rick Wakeman plays Mellotron on two songs.
Scream: Gus G. plays guitars, while Adam Wakeman (Rick Wakeman's son) plays keyboards.
Keep Circulating the Tapes: The album The Ultimate Sin has been out of print since 1995. No official reason for this has been given, but it's widely believed that it's due to an unresolved legal struggle between Ozzy Osburne and songwriter Phil Soussan over the rights to the song "Shot in the Dark."
One of Us: Blizzard Entertainment hired Ozzy for a commercial for World of Warcraft. He likes it. They gave him his own character model.
Blizzard of Ozz and Bark at the Moon features Don Airey on keyboards before he played for Deep Purple.
After his tenure in Ozzy's solo band, Tommy Aldridge went on to take part of Whitesnake alongside his fellow bandmate Rudy Sarzo.
Randy Castillo went on to play with Mötley Crüe until his death.
The Red Stapler: Randy Rhoads' use of a 1974 white (which aged to a creamy yellow) Gibson Les Paul Custom has resulted in prices for said instruments being higher than most other Les Pauls of the era, which are generally looked down on as inferior instruments to earlier and later eras.