On my first playthrough either Pichu, or Elekid hatched from it (dunno which one though xD) and on my second playthrough I got Tyrouge. I remember, because I wanted a Hitmontop so bad and when it evolved, it became exactly this Pokemon. I was so happy
I have no idea what hatched my first playthrough of Crystal because it's been years and that file is long gone. But on my second playthrough I hatched a Shiny Elekid. Though I didn't even know it was shiny until I brought it over to Pokemon Stadium 2 where I then went 'WAITAMINUTE......'
Then with the latest Crystal playthrough I did on an emulator I hatched a Shiny Magby.
The first time I hatched it, I think I got an Igglybuff. I restarted the game every time i hatched it because my main goal was to get a Pichu from the egg. I'm pretty sure I got every Pokemon that could hatch out of the egg BUT a Pichu. Just my luck.