I too have been on a quest for getting the absolute best rate at the Grand Californian. I've been doing a lot of research, and asking a lot of questions, and these are my findings...
Annual Pass, AAA and Disney Visa discounts are only 10% off the "rack" rate. You can most likely get a better rate if you are patient and can stay informed on periodic specials.
"Special" Annual Pass room rates are given occasionally. Right now this rate code is "AP7" and it's good up through Dec. as I understand. I'm hoping that once this promo expires, they'll offer another one (possibly AP8 or other.) I've also heard of "pin" codes that people have randomly received via snail mail or email.
Having an AP seems to be the best all around way to get a deeply discounted room rate. If you do not already have an AP, you can still book any AP rate as long as you purchase one when you arrive (which you can do at the front desk upon check in.) One problem with this scenario, is that you will not personally receive AP notifications of any "special" rate (or have access to the AP website), so you'll have to keep your eyes peeled here on these message boards or elsewhere.
Expedia.com will often have rooms available at 50% off the rack rate, depending on your travel dates. You will have to wait until closer to the time of travel and I've heard the very best rates are given approx. 2 weeks before your check in date. I've heard that this is the single best way to receive the absolute lowest rate possible.
Keep in mind that if you purchase a package, the cancellation policy will most likely have different terms than a room reservation on it's own. My room only reservation can be canceled within 5 days of travel, I've hear that packages carry a cancellation penalty. Generally, you will do much better all around by NOT purchasing a package.
Obviously, Holiday's, weekends and peek season at the DLR are going to be the most expensive times to stay. Sun. through Thurs., in off season will be the cheapest.
Check out this site for some really helpful and specific info pertaining to this subject:
http://www.mousesavers.com
(go the the
Disneyland - DL Resort Hotels section)