There's a massive amount. His writing credits spanned from Blues Away to Best of Joy, and there are many tracks which we don't even know about, hidden in the vaults. He's credited for eight of the ten tracks on Michael (everything except HMH and AD). Then there are his poems, handwritten lyrics, material recently registered by the copyright office, songs he wrote for other artists, songs which evolved into others... For example, Much Too Soon and Learned My Lesson are registered as two separate songs, when in fact they are the same.
I'm sure there's a list of released material he has writing credits for (for solo songs at least), so I'll try and find one.
Blues Away
Don't stop Til You Get Enough
Working Day And Night
Heartbreak Hotel
Sunset Driver
Wanna Be Startin Somethin
The Girl Is Mine
Beat It
Billie Jean
Bad
The Way You Make Me Feel
Speed Demon
Liberian Girl
Another Part Of Me
I Just Can't Stop Loving You
Dirty Diana
Smooth Criminal
Leave Me Alone
Fly Away
Streetwalker
Lisa It's Your Birthday
Heal The World
Black Or White (minus the rap)]
Who Is It
Will You Be There
Do You Know Where Your Children Are
They Don't Care About Us
Stranger In Moscow
Earth Song
D.S
Money
Childhood
Little Susie
Morphine
Speechless
The Lost Children
The way You Love Me
Best Of Joy
Much Too Soon
and i'm sure there's a lot more that i missed
Wasn't the P.Y.T demo also written by him?