I have a '99 300M with 105,000 miles and a new brake job. It has just started vibrating when I am braking, whenever I get to slower speeds or when I brake suddenly. I don't know if it is a brake issue or maybe a tire balance issue.
Front rotors could need replaced if not already. If not replaced yet have them turned or replace them with high quality parts. Newer cars run better with better than basic parts. I put cheap rotors on my 03 stratus and two days later I put the best that the parts stor had on because of the shaking : )