I am slowly getting an A1K up and running. Currently it is stock with the 256K memory in the front for 512K. I have noticed I some games complaining of not enough memory (Wings) and was looking at what was available currently.
m68k
8 Meg upgrade using CPU slot. Same person also sells IDE interface that stacks with the memory upgrade
ACA500+
8 Meg ram, compact flash hard drive, accelerator and kickstart rom. Can be flaky on the A1K and is not officially supported. Yet.
Terrible Fire 530 (TF530)
2 Meg ram, IDE, 68030 CPU. Requires kickstart ROM
Wicher 500i
Up to 8 Meg ram (72 Pin Simm), IDE, CPU Accelerator. Hard to find stock.
Am I missing any?
Yes there was:
Vampire 500+
128 Meg ram, Compact flash IDE, accelerator, kickstart rom, AGA upgrade. Uses hardware emulation to replace original amiga chipset and CPU using the original amiga as a keyboard and mouse.
Upcoming:
Rejuvinator
Currently being reverse engineered. Originally allowed for 1-2 meg of chip ram (depending on which upgraded Angus is used), kickstart rom, upgrade to ECS, only for amigas with WCS daughterboard.
ace1k
Adapter to allow upgrade chip ram to 1 or 2 meg. Expected in 2019.