The best dry foods on the market:
Applaws dry cat food (more protein than any other dry food in existence), but I've abandoned this stuff as it gave my cats loose stools.
Orijen dry cat food (the 2nd highest protein content dry food; it also won the 'pet food of the year' contest).
Hills Science make some good dry foods, but personally, I think their foods are overpriced and though good, don't compare well to the 2 dry foods mentioned above.
For wet food, I have settled on Tesco Luxury Cat food (about £3 per kilo), 50% meat content. I also mix this up with Whiskas cat food.
Other top quality premium wet foods include Nature's Menu (70% meat content), which is what I gave my 2 when they were younger and HiLife (60% meat content).
What you are looking for is the food with the highest meat/protein content in it. Typically Whiskas will have about 4% meat content, while the best wet food that money can buy (Applaws), has about 70-80% meat content. That stuff is way too expensive for a cat, though.
In general, the higher the percentage of meat content in the wet food, the more pricey it is, which is why I'm surprised that Tesco Luxury Cat food is so cheap, in comparison to other wet foods of similar quality.