Arma 2: Invasion 44
If any of you guys haven't seen it there is a World War Two mod out for Arma 2 called Invasion 44, it's pretty well done and is still being worked on, however the next release of the mod is unknown due to the loss of many of the staff and only consists of a skeleton mod team currently. It's a really great mod, however it is lacking a dedicated server to run on. Also as a side note this mod is for Arma 2 currently not CO or AO, that is something they are working on fixing for the next release.
Here's the link to the website:
Also here is a youtube video of some game play: Note this is gameplay of the beta of the newest version of the developers are currently working on