Currently, DVC members get a $100 discount on annual passes. DVC members will get various discounts on the non-peak MK "party" nights (MNSSHP, MVMCP, etc.). Also, there is a DVC discount with several restaurants, including those in the parks and in the resorts, as well as discounts at various retail shops and discounts on other entertainment (boat rental, etc.). DVC releases a booklet with the discounts and they are, of course, always subject to change.
Just keep in mind if you're factoring perks into a decision to purchase that perks change & sometimes are removed altogether; they are not guaranteed & there is no stipulation that there will be any sort of perks offered to DVC members so any and all perks can disappear completely.
Like 5forDiz said, don't buy DVC for the perks. Or for trading out. They change all the time and often just disappear never to be seen again. For example, DVC members used to get 10% off length of stay passes. No more. The points to cruise used to be a whole lot less. Trading company use to be II and before that RCI. Now it's RCI again. But not all of RCI, just select locations. We used to be able to pool hop to SAB. No longer.