My deli of choice in North Oxford has to be Gluttons, if not for the stuffed vine leaves at 20 pence a pop, then for the delicious staff. Treats for both the tummy and the eye.
The deli is located on Walton Street, and do the best Tiffin in town. They also stock a wide variety of 'hard to get' items. They will try and order in anything you cannot find, and even though it's quite pricey at times, it's well worth a visit, if only for an inspiring browse.