Baseball ought to get instant replay. They are discussing it for only homers, which is STUPID! There are plenty of questionable calls made at the bases, and I think instant replay would ensure the old farts umping would get the call correct.
I would make it so that if the ump's don't know for sure what the call is, and this would require great integrity on their part to admit that they didn't see it well enough, that they can defer to instant replay.
Also, I would give each manager two times they can call it per game, but if they are wrong, they get charged an out. Like in football, if they are right twice in one game, then they do get a third in that game. If they are awarded the third for being correct the other two times, and they use the third and they are wrong, then they would not be charged the out on the third replay attempt, that's their freebie for being correct the other two times.