I don't know much about the tcgplayer.com API (which I assume is what deckbox.org uses) but I have some promo cards that I'd like to add to my DB. eg.

http://magic.tcgplayer.com/db/magic_single_card.asp?cn=Plains%20-%20Guru&sn=Guru%20Lands
http://magic.tcgplayer.com/db/magic_single_card.asp?cn=Emrakul,%20the%20Aeons%20Torn&sn=Prerelease%20Cards

Right now you can kinda denote a promo by hitting the promo button but it seems like there could be more refinement above and beyond that. Whether or not the tcgplayer.com API supports promos is one thing but tcgplayer.com certainly has them listed on their website..

+1

I agree with this Wholeheartedly.
I know TCG Player is gone now, but with all the work being done on the website.. maybe now is a good time to add FNM Promos / Full arts / Artist Proof option / general promo foils.

Always sad when I see an incorrect price on promos and have to refer to various websites to declare value.
One specific noteable is the buy a box promo for Rise of Eldrazi; Emrakul, the Aeons Torn.

Regular Midrange: $49.99
Regular Foil Midrange: only one listed on TCGP @ $199.99
Buy a box Promo Foil Midrange: $38

I have seen it quite a few times, people listing it as set: Eldrazi, Foil, Promo.
promo not effecting the price and a BaB promo showing up as ~$200.
And some people using that listed value to inflate the actual value of the card.