Too many great games to have a single favorite, but here are some I remember.
Pushover (came with the A600 Wild, Weird and Wicked pack).
Grand Prix
Super Skidmarks
Lemmings
Ishar 3 AGA
Sim City 2000
Cannon Fodder
Stunt Car Racer
Worms Armageddon
Turrican 1, 2 and 3
Ruff N' Tumble
Walker (in two player)
Project X
Genetic Species