There are a lot of AGA games that will run perfectly well on an unexpanded A1200.

You could do a search on classicamiga for AGA games and find them all.

Here are some I like:

Arcade Pool
Alien Breed: Tower Assault
Banshee AGA
Brutal Sports Football AGA
Bubble and Squeak
Civilization AGA
Colonization
Capital Punishment
The Chaos Engine AGA
The Chaos Engine 2 AGA
Diggers
Dreamweb AGA
Exile AGA
Gaurdian AGA
Jungle Strike AGA
Jetstrike AGA
Gunship 2000
Impossibe Mission 2025
Legends
Liberation
Napalm
Nigel Mansell's World Championship
No Second Prize
Overkill
Pinball Fantasies AGA
Pinball Illusions
Road Kill
Simon the Sorcerer AGA
Skeleton Krew AGA
Super Skidmarks
Super Stardust
Slamtilt
The Speris Legacy
Total Carnage
Theme Park AGA
UFO: Enemy Unknown AGA
Uridium 2
Virocop AGA
Worms AGA
XP8 AGA
Zool 2 AGA

And with an HD and some fast ram I highly recommend Star Trek: 25th Anniversary, Gloom, Fears, Breathless, Alien Breed 3D 1 and 2, and Sim City 2000 AGA.

I think that's a big enough list to keep you going