I learned this on a food tour in Seattle and I really want to share! There are probably people who already know this, but I am sure there must be some who don't :-) (I sure didn't know!) :
Choose a male eggplant. Males have less seeds, so they will be less bitter.
How to know if your eggplant is male or female? Look at the bottom. If there is a brown circle it is a male. If there is a long brown mark (like a slash) then it is female.
Pretty neat, huh ;-)