There is definately one place you should go for custom COD4 maps!
I didn't believe my eyes when I found this page yesterday.
172 tested and rated custom maps with filter function and map rotation generator.
Link: Call of Duty 4 - Maps & Mods

I wish more MP games would do what Valve did with CS 1.6 and CS:S. I am honestly bored with about half the maps in COD 4 right now and I really don't see myself playing that much longer. I played CS 1.6 and Source both for years. Why? Because 1.6 had about 20,000 maps and Source had at least 5,000. Yes 85% of them were crap, but that still left you a hundred times more maps to play one than any other MP game I can think of.

Ironically one of the best games for new maps after release was Lost Planet for the 360. Lots of people didn't like the MP but I loved it. Over a period of about 12 months they released about 15 new maps and then capped it off with LP Colonies which added more maps, 10 or more new MP modes, and 4 or 5 new weapons.

Hello??? Is anyone listening??? This type of support is what a lot of gamers, both PC and 360, would like to see and it really pisses me off that more companies don't do this. Instead they blame there crappy games lackluster sales on piracy and then go back and make another crappy game expecting a better result. It's an absolute joke.

I'll be honest I have and will continue to pirate video games that I don't want to take a chance on. I have too many games collecting dust already and I'm sick of wasting my money. WIll I buy it if I like it? Of course. I own COD 4, Bioshock, Mass Effect, Quake 4 and I have bought and traded so many 360 games it's disgusting. But if all I'm gonna get is a game another game I can't get my money back for (PC) or another 360 game I have to trade in for $10 bucks when I paid $60 they can kiss my ass.

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Durka! Durka!