I upgraded my plugs to Champion 7989 from Rock Auto Parts and they sent me a 5% discount code to share with "friends". They already have the lowest price I could find on the plugs so here's to getting them even cheaper!

Discount on RockAuto Parts!

Thank you for being a www.RockAuto.com customer! To show our appreciation, we have a special discount for you.
Your discount code is:
1074789940507

Using Your Discount Code
Enter the code above in the "How did you hear about us" line of the shopping cart. If you are using our traditional HTML catalog, please click the "Apply" button to the right of the field. Your discount will automatically appear, subtracted from your order total.
Please note: We sometimes get calls from people who put the word "discount" in front of their code and do not get the discount. Please enter ONLY the discount code, no other words or numbers.
The discount takes 5% off our already-low prices. There's no limit on order size or the number of orders. Use the code for your next order, and share the code with friends, neighbors, relatives, the guy at the corner garageanyone you know who works on cars or trucks.
This discount code expires on August 5, 2008; so don't wait!

 

Can't seem to locate the plugs on their website? Search doens't yield any results?

 

From the main catalog search I drilled down from Ford -> Mustang GT -> 4.6 -> Ignition and there they are.