what's the best way to work out your inner chest so that it actually has that dividing groove? I've had a fairly weak chest all my life, but it's been getting better lately. So if anyone knows of a good inner chest work out that gives good results, please share.

It's mostly genetically dependent how your chest looks like when you've added mass, but dumbbell flat and incline bench will allow bigger range of motion compared to regular bar, so I would assume you can use that.

Instead of focusing on the "groove", I'd recommend just focus on adding mass to your chest in general. To gain mass, here are the the best:

1. Bar Benchpress, flat
2. Bar Benchpress, incline
3. Bar Benchpress, decline

and secondly

1. Dumbbell Benchpress, flat
2. Dumbbell Benchpress, incline
3. Dumbbell Benchpress, decline

The only workout I do for my chest is pushups, and I have better cleavage now with 34AA than I had with 38C!

Of course, if you're a guy, you're probably much different.

Get breast implants!

Ok, some smart ass was going to say it eventually so I thought I would be that smar... I mean get it out of the way.

Do what Duckman suggested. I now don't do barbell bench press since dumbell bench press rules in adding mass.

I've made pretty good progress doing the following:

Flat DB Bench Press/Incline BB Bench Press/DB Incline Flys/BB Pullover

don't forget about weighted dips!
(leaning forward slightly for focus on chest)