I am looking for a manufacturer of after market brake pads and clips where the pads and clips ACTUALLY FIT so that the pads don't chatter. Anyone who has had luck not paying the premium on OEM pads and clips, I would love to know the where to buy them.

 

EBC brakes

 

While not cheap these are super quite, and almost no brake dust. I purchased for my 04 4.2l and I love them. Available on Amazon for quick delivery

Akebono EUR1065 EURO Ultra-Premium Ceramic Front Brake Pad Set For 2003-2005 Jaguar S-Type
Akebono EUR806 EURO Ultra-Premium Ceramic Rear Brake Pad Set
Ultra-Quiet - controls noise, vibration and harshness level
European braking performance with enhanced pedal feel
Extremely rotor friendly for longer rotor life
Friction formulas specially designed for European vehicles

Also for standard suspension at amazon as well
Centric 125.61060 Front Brake Rotor
Centric 125.61062 Disc Rear Brake Rotor
Centric are Premium High-Carbon Rotor's, without the name brand mark-up.
My Father has used Centric for all our family's auto's for almost 10 years, He owns both a 03(purchased in 04) and 06(purchased in 08) Ford SUV's that OEM rotors would warp after getting them turned or repeated heavy braking,, the high carbon content can take abuse without warping. While Brembo, EBC and others, make great rotors, at 3 or more times the price of Centric, which work just as well as the Brand name at a huge cost savings
For DIY'ers truly best performance for your buck, For Rotors verify your Jag's suspension type standard or sport, as they are not interchangeable.