Has medical progress stopped human evolution?

Keep in mind that most people live in environments where antibiotics are of limited availability and hygiene is not as rigorous as in the "western" world. Combine this with high population densities and you get, if anything, more natural selection due to the spread/proliferation of pathogens and the subsequent mortality of the patient.
Also, don't confuse natural selection for evolution. Natural selection is one of only five causes of (micro-) evolution. Mutations will continue to occur. Sexual selection continues unabated, and migration is more important now than ever. The only evolutionary factor I'd argue is being diminished is genetic drift since there are so many people today.