I strongly recommend Spycraft Espionage Handbook (core rulebook), Modern Arms Guide (weapons and firearms supplement), and Soldier/Wheelman Class Guide (for use with the two core classes that are military-oriented).
Also, check out Afghanistan: d20. While many gamers avoid this supplement out of respect, the authors (Gulf war veterans themselves) wrote the game supplement with sensitivity in mind yet provide a good description of the region with game rules to play, including a US soldier. It's also cheap: $20 for the softcover product.