I wrote
this article on Mac|Life that lists 10 classic Mac games you can play on iOS, following a chat with Niemann that stemmed from my discovery of Spaceward Ho! for iPad.
But there are a lot more than 10, so I thought we could list them all here.
So there's the ones in my article:
Spaceward Ho!
Glider Classic
StuntCopter (which has a new feature-complete iPad version)
Crystal Quest
Spectre 3D
Zone Warrior
Myst
Marathon 1
Spin Doctor
Otto Matic
plus:
Riven: The Sequel to Myst
The Manhole (unfortunately the remake, not the original)
Prince of Persia (Mac version was ported but has since been removed)
Bugdom 2
Cro-Mag Rally
Nanosaur 2
Enigmo 1
Enigmo 2
SimStapler
Jared
Glypha
Marathon 2: Durandal
Yoot Tower (SimTower)
AliceX (Alice aka Through the Looking Glass; no longer available)
Any others?