jayananda asked about this on an older post, so here it is:
Submerge peaches, no more than 3 at a time, in boiling water. Boil for 30 sec- 1min. and remove; let cool. The skin should easily slip right off. Then, to pit: slice around the middle of the peach lengthwise, along that neat little line provided by nature. Twist the peach halves gently; if it's a freestone peach, the halves should easily separate. One half should now be pitless, and the pit can be easily pried off the other half*. If it's a clingstone, you'll have to slice the peachy goodness off of the pit, losing some juice on the way.
This time of year, around here anyway, we mostly get freestone.
(*Note: sometimes, the peach pit decides to split in half, too. Annoying. Just pry it away.)