Letter - Letter domains carry the same rarity as two letter domains (676 possibilities), but not necessarily the same value (yet).
I like I-P, but don't see much instant-value in the .biz. Maybe $20-$50 wholesale, or much higher to an end-user (like stated above "intellectual property" lawyers, or even an ISP, "internet protocol).
What I would do is flirt with the market, see what some people would offer you for it, if it's reg fee to $50, I'd hold onto it for awhile, stick it in the vault. I'd hate to sell it to somebody for $20 one day who sells it for $200 a couple months later.