I imagine this is pretty basic, but I haven't seen any code posted here to calculate the median of a list of numbers.  Here's mine, which could pretty easily be adapted to most uses:

List<Integer> testvalues = 
   new List<Integer>();
Double Middle;

testvalues.add(1);
testvalues.add(2);
testvalues.add(3);
//testvalues.add(4);

testvalues.sort();
decimal sizeOfList = testvalues.size();
system.debug('size of list is '+ sizeOfList);
Middle = sizeOfList.divide(2,1);
system.debug('middle of list is ' + Middle);
system.debug('minimum value is ' + testvalues[0]);
system.debug('max value is ' + testvalues[testvalues.size()-1]);
//Calculate median
	if (middle <> middle.round()) {
		system.debug('median is '+ testvalues[middle.intValue()]);
		}
		else {
		decimal lowMedianValue = testvalues[middle.intValue()-1];
		decimal highMedianValue = testvalues[middle.intValue()];
		decimal Median = (lowMedianValue + highMedianValue)/2;
		system.debug('median value is ' + Median);
		}

 I hope that makes someone's day easier.

Baird