Assuming you are an adult, you'll typically look for a 28oz/34" softball bat. Other than that, it's based on how much you want to pay. I bought a Nike 30oz/34" softball bat that was on sale for $40 (from $80) and I feel like it hits just as good as the $300 28oz/34" softball bat my team coach brings for our games.
I'm not a pro, though, this is my first year of playing softball. Still learning myself. I do know one thing though.....playing softball in an organized environment is one of the most fun things I've done in a while.