Just to add to ericmwalters post, ProSimCo has recently released a new tactical level simulation called Air Assault Task Force (AATF). While ATF and its follow-ons are more suited to armored warfare, AATF focuses on light infantry. The game has scenarios based on LZ XRay (I think...the we were soldiers battles), Mogadishu, and Operation Anaconda. It probably comes a bit closer to COIN type operations than ATF, but I wouldn't say it's there yet.

Here's a link to the website: http://www.prosimco.com/

There's a free demo available as well.

Take care,
Brian