Just my newbie 2 cents:
1. It would be MAGNIFICENT if my customers could enter text to have their items personalized - ie, a name to be embroidered or a last name/number to be put on the back of a jersey. I'm currently using a form within the listings, but customers are leery & confused...not a good combination when trying to pry money from their wallets
2. Shipping Cost - regular shipping costs until the order reaches x amount - then free shipping.
3. Ability to click on a "show me link" or something similar to see color options or font options.
I'm running SCCP, if these functions already exists, I haven't found them yet...but they'd REALLY help me out