I'm kinda partial to the valentini puffer myself. I have one in my 75 and he is perfectly content. It's cool watching his eyes move independantly as they survey the entire tank. I've been thinking about getting a blue spot to go in the tank also. As far as a good fish to go in your 75 I would recommend any of the canthigaster species. If you want a bigger puffer you could go with a spiny box or dogface which are pretty interesting fish also.