The more money you pay, the fewer blockout days you have. You get food discounts with all APs, but I'm pretty sure only the Premium has a merchandise discount. The Premium is also the only one which includes free parking; if you want free parking on a lower pass, it's an additional fee (used to be $49, might have gone up). Those are the main differences, though it's been a while since I've had an AP, so I may be misremembering things.
Cinderella IV: The Bloodening
"It's okay, Beaker, we're scientists. We get paid to fail."
^ They have selected dates called "AP Nights." You should call the specific hotels and ask them about it. I haven't use that benefit yet. Maybe someone can post how much of a discount AP's actually get.
As for the Premium AP: 10% on merchandise, 15% on food, free parking and of course 365 days entry!
Disneyland Annual Passholders get meal discounts at Disneyland Resort. Unless otherwise specified, discounts apply to the Passholder and the Passholder's dining party. Not valid at outdoor cart locations, snack locations, Club 33, Napa Rose, and Room Service locations. Dining discounts are not valid in combination with any other discounts or promotions and exclude alcoholic beverages, tax and gratuity.
Southern California Select Passport, Southern California Annual Passport and Deluxe Annual Passport holders get 10% off meals at virtually all dining locations, including most Disneyland, Disney's California Adventure and Disney hotel restaurants, as well as Downtown Disney restaurants.
Premium Annual Passholders get 15% off meals at virtually all dining locations in Disneyland, Disney's California Adventure and Disney hotels, and 10% off at most Downtown Disney restaurants.
Disneyland Annual Passholders get nice merchandise discounts at the Disneyland Resort. A single $10 transaction required before tax. Not valid in combination with any other discounts or promotions or on purchases of original and limited-edition artwork or selected collectibles. Excludes the following locations: Names Unraveled, Jewel of Orleans, Silhouette Artist, Portrait artists in New Orleans, Parasol cart, Heraldry shop, Crystal shops on Main Street and in New Orleans and Blast cart.
Premium Annual Passport holders get 10% off merchandise at most shops in Disneyland, Disney's California Adventure and Disney hotels as well as Downtown Disney shops, including World of Disney and Marceline's Confectionery.
Southern California Select Passport, Southern California Annual Passport and Deluxe Annual Passport holders get 10% off merchandise at most Downtown Disney shops, except World of Disney and Marceline's Confectionery.
Annual Passholder Rates (HOTELS) - Annual Passholders may qualify for discounted rates -- call and ask for "Annual Passholder Rates." The general discount is 10% off rack rates, and sometimes there are specials that are more deeply discounted (generally in off-season, like September, October and January). Discounts are not always available, particularly during peak periods (all holidays, summer). Rates are lowest on Sunday-Thursday nights. The very lowest rates are typically offered about a month in advance. Limit 2 rooms per person at discounted rate. Be sure to check the Expedia rates below, which are sometimes LOWER than the Annual Passholder rates.
Also, the Howard Johnson on Harbor gives a 15% discount off their lowest rate to AP holders...