Well, i noticed that with cod4 there are not really that great stats around. With CS:S HLstatsX is the big thing and actually i was looking for something like that. We use currently Ultrastats which displays kind nice the top users with medal's.
but its still beta, so not everything works that well.
I personally like to have php based stats, since i can run it on our webserver. Statsgen is nice, but takes horrible long to compile the stats and rank the players. so you want to run it only once a day. and its windows only which is, as already mentioned, kinda bad if you don't own the server rig.