Im new to the Amiga 1200 (Always was an Atari man, but really nice to try a "new" computer out) but what i find hard to get hold of, or very expensive:
A 68060 accelerator board for sure. Superb if it used sdram. Would be a dream.
Second on the list would be a flicker fixer. Afaik u cant buy an indivision for the 1200 anymore.
But ppl here have given loads of good examples.