Its Gamespy's stats, by players.
I have updated the original list., and attached it in excel format as well which is easier to read.
I have also extracted the HALF LIFE sub sections and merged them with the main list, which shows how populAR Both hl1 and 2 mods are!
The list is sorted by most players, then by player/server ratio and then just name.
Why?
I wanted to know what the ratio of players to servers was.
More suprising than I thought, COD4 has an unreal low ratio of 0.4 players per server.
Compare that with other games with similar player numbers.
5 HL1:DayofDefeat_______________5.6
3 Wolfenstein:EnemyTerritory_______2.4
7 HL1:Counter-Strike:ConditionZero__1.8
4 Battlefield2____________________1.6
6 CallofDuty4:ModernWarfare________0.4
What this means is that you get a few servers with lots of players, and lots of servers with a few or

players.
(THIS I BELIEVE IS A CURRENT SNAPSHOT OF PLAYERS - IE Midday on a thursday.)
Amazingly, Counterstrike for HL1 is still the top game. And HL2:CSS is close second. Between the two of them, they dominate the entire table, being about 5 times higher than the 2nd or 3rd place each... and 10 x between them (if you class them as effectively the same game!)