We booked our package last year through AAA (saved us about $200.00) and are booking through AAA again this year.
In addition to the package savings, you also receive the parking pass as others have mentioned. If you're driving, this pass is worth its weight in gold (at least my DH & I feel this way)! We rode the monorail to Epcot & the boat from FW to MK, but we were able to park so close to AK & MGM - we just walked to the entrance w/o waiting for the tram.
We also got a 10% off purchases from World of Disney in DTD - which saved us about $50!
And, if you book a Family Magic Tour in MK, you get a 15% discount. At least, this was the case last year - not sure about this year. I think there were some other things that we could have received discounts on as well - like golf & some other tours.
We didn't use the AAA lounge last year so I can't comment on that. This year, we're considering the AAA "Story w/ a Character".
I think that January is "Disney Days" at AAA, and, if you book a package through AAA in January, there are some more perks as well.