DD and I are vegetarians (dd is semi-vegetarian, she eats chicken maybe once every 2 months or so) and we do not drink cow's milk. We do eat cheese and yogurt but too much of any dairy product gives dd constipation really bad. The dairy industry (and common folklore) wants people to believe that cow's milk is necessary for good health, but they are wrong. There are so many other ways to get calcium in a much healthier way (green leafy veggies for one, fortified OJ for another---though fortification is debatable).
Water is the #1 drink.
I like to remind people of what mother cows go through to produce the nation's supply of milk. It is absolute torture. And we are drinking all the hormones pumped through their bodies so they'll overproduce. If I have time to dig up a link, I'll post it (or anyone else here please feel free). The only reason to drink milk regularly is to fill the pockets of the dairy industry. If you have to drink cows milk, at least drink organic hormone-free cow's milk from a dairy that treats their cows humanely.