Plasticine v. good, especially the breaking bits off and rolling.
Buckaroo - but ds2 found it a bit stressful.
Hama beads would be good, but still too fiddly for ds2 (9)
Squeezy balls he quite liked, just for building up strength in his hands.
I used to give him scissors and old wallpaper samples to cut out - so he didn't have to cut along a line, that came later. He could just get used to the cutting without the stress of doing it properly if that makes sense.
Big cotton reels and big laces more successful than threading beads.
Now he's older - I have discovered a fascination for BATTLESHIPS just because it gets him putting the beads on pegs.
At 4 - we did loads of drawing with chalk outside, and old big rolls of wallpaper (again) to get big actions going in his shoulders.