Vick and Roethlisberger are basically in the same situation, early in their career and they've accomplished a lot already, but making/winning the Super Bowl would be huge for either of them. But its not really a lot of pressure.
Brady has a bit of pressure on him in the form of getting his team back to the Super Bowl for the 3rd time in 4 years, and the fact that he's still not lost a playoff game.
But I think McNabb has the most pressure on him. How many more Championship games can he lose in a row before it becomes an "I know Im gonna lose this game, it doesn't matter.." syndrome. Surely hes not going to lose his job or get traded, but eventually the Philly fans will have to turn on someone, and who better than the guy with a $115 million contract that cant win a big game? People talk about Peyton Manning choking all the time, but is there really a bigger choker than McNabb? Lead your team to 3 division titles..and then lose 3 Conference Title games in a row including 2 straight at home.