Aaaaaand here's what I've got going for the SEGA stuff...
I started out with the Genesis striped style, because I didn't grow up with Sega stuff and most of my exposure to the system was later on once they'd taken up that style. Heck, out of my Genesis games I own right now in the original cases, three are striped. The only one in the older grid layout is actually a Mega Drive game

... And then I've got two that aren't in either format. Sega cases are sort of all over the place with their styles.

I went with the white "GENESIS" instead of the silver because, let's face it, it looks better. The SEGA in the upper right is intended to match the SEGA on the top of many of the original cases.
But, like
wiggy, I thought it'd be better if the stripes continued across the spines when all set on the shelf. Instead of going to custom stripes at a 45 degree angle like his, though, I tried to keep the original angle and adjust the size of the stripes to fix it...

... I don't know if it works nearly as well.
Next, since I was going to have to do a grid design for the Master System anyway, I figured I might as well tackle the Genesis grid first:

Then I thought... "Maybe that logo would look better monochrome?"

Ooooh yeah, that's the stuff! The grid on these isn't an exact match for the original retail grids. Rather, it's designed to continue across the spines on the shelf and it's lined up vertically to "cut off" the banner on the front.
Next was Master System.

It's Master System. Simplicity incarnate. But, I figured I'd try one more thing... Master System cases that match the carts?

Eh, cool in theory, but I think we'll stick with the white grid.
Still have to vector up the controllers and such.
Well.... Thoughts, suggestions, other input?