Any suggestions on a display case for a Mosin Nagant 91/30?  I tend to lean towards the cherry-colored wood, but besides that... any recommendations?

1. Buy Mosin crate
2. Replace lid with glass
3. Fill inside with Mosins
4. ???
5. Profit

Add the bayonet, ammo pouches, a couple of stripper clips of ammo, the lid off a WW2 vintage ammo spam can, and a M1895 Nagant revolver with holster. Make your background the USSR flag.
If you use the 91/30 only, you'll end up with a really long and skinny display case, which will look quite odd unless it fills a particularly long, skinny bit of wall space.

Or just build the Mosin crate coffee table and call it a 10-rifle display case.

Case wood should complement the rifle stock wood (either by matching well or providing a nice contrast) without clashing with the background.
The background can be plain, but usually has greater visual impact if it's something that both relates to the object in question, and that the object stands out from visually, i.e, doesn't blend in with it.

I'd use the USSR flag if you want to just have a 91/30 (and maybe the M1895 Nagant).
Other examples: A 91/30 PU sniper would look nice on a background of WW2 Soviet camo - they contrast. OTOH, an FDE-painted M-4 on a background of desert camo would blend in and visually suck.  

If you use only the 91/30, I'd make the case wood match the stock color as closely as possible. This might be difficult.
If you add the Nagant, get one with blonde grips. Using a similarly-blonde wood for the case would pick up the little bit of blonde wood on the Nagant, and contrast nicely with the darker red-brown of the Mosin stock and the crimson of the USSR flag.

DING!

Good advice.  Thanks.

My local Gander Mountain has Mosin crates for sale for $150 each!!!