I've been map testing for a guy called Hayabusa for several years now. He created over a hundred maps for the battlefield series; some of which are amongst the best free custom made maps available for that game. He recently started modding and mapping for the first person shooter game called Crysis. So far he's released several maps, each one getting better thab the last. He's still getting to grips with the editor. I thought I'd post a link to his site so that you can check out the maps yourselves. I'll be writing reviews for each one over the coming months. His most recent release is called Jungle Warfare and is in my opinion one of his best so far (together with The Gorge) He's even created one called
For anyone who hasn't heard of Crysis, but decided to check this thread out anyway, it's probably the best FPS game (together with COD4) to have been released to daate. It's got unbeleivable graphics, a partially destructible environment and a decent story line. The game isn't quite a snadbox game, but it's close. The only down side to the game is that you do need a decent gaming rig, with a decent graphics card. The gam,e supports DX10 graphics and is moddable.
I'll probably post details of other maps and mods when I have time, but for the time being I highly recommend you download Jungle Warfare and 'Get Some In'
You can only find it at the following place at the moment. to download it you will need to register, but it is totally free and only takes a few moments:
http://bf2mercenaries.freephpnuke.org/ (site no longer operating)