To say that we have halted evolution would be quite incorrect.
Taken in its broad sense, biological evolution is basically change in allele frequencies from one generation to the next. This is regardless of natural selection (NS), however NS is one of the main (and certainly most famous) factors contributing to evolution.
Genetic Drift (GD) is also an important factor in evolution. Still though, evolutionists argue over which contributes more - NS vs GD.
Basically, GD refers to random (a better word, stochastic) changes in allele frequencies from one generation to the next, depending on who contributes "gametically".
This argument aside, as has been said, recent work has shown that humans have been subject to NS during the past few thousand years, at least.
When it comes to medical advances, while it is true that they have resulted in the possibility of saving more lives, as Crash has pointed out, this happens mainly in the first world, and most people on this planet don't live first world lives. Actually, the March of Dimes has recently released its
global report on birth defects. It's clear that these are still a serious problem.
At the most, the filter has been removed (as Jar said), meaning that the possibility of these "affected" people contributing to the next generation is now higher, since they've not been killed off by their affliction. However, it should be noted that the majority of disease alleles are present, not in the afflicted, but in "healthy" carriers, and so would still possibly be passed on regardless of whether or not the afflicted survive to reproduce.
And still while we have affected the environment, we still have to live in it. Many of the things that have been done, have been inadvertant, and so still could exert selective pressure on us in the future.
To sum it up, evolution doesn't stop with the removal of NS; which arguably, has not been removed.
"The good Christian should beware the mathematician and all those who make empty prophecies. The danger already exists that the mathematicians have made a covenant with the devil to darken the spirit and to confine man in the bonds of hell." - St. Augustine