I agree with sleeptalker, raw is the best way to feed in my opinion. Here's some good links:

UK BARF Club - The Ultimate BARF and Natural Feeding Guide for Cats and Dogs
The Many Myths of Raw Feeding
Jane Anderson's Raw Learning Site

and the threads on here:

Why Feed Raw?
Raw Feeding Discussion
Raw Diet

and these are some good books:

The Barf Diet: For Cats and Dogs: Ian Billinghurst
Natural Nutrition for Dogs and Cats: The Ultimate Diet: Kymythy Schulze
Raw Meaty Bones: Promote Health: Tom Lonsdale

If raw isn't for you Orijen is the best dry food available in the UK, it's 70% meat, 30% fruit & veg, no grains/cereals or artificial additives, preservatives etc.

James Wellbeloved is also a good quality dry food, they do a couple of grain free varieties and also a variety of good quality pouched wet foods.

Naturediet (mentioned above) and Natures Menu are good quality wet foods.

Pedigree and Bakers are terrible foods, IAMS is not great either and has been linked to some horrible animal testing in the past. A general rule of thumb is to avoid anything you can buy in a supermarket.