So you've just finished Command & Conquer and fancy a go at the real thing, but you need to find out MORE than you should about other countries for a greater campaign? You'd be amazed at the amount of information you can get online. Size up that small country you've wanted to invade since finishing Civilisation II.
UK Military of Defence
http://www.mod.uk/ 
Whitehall's home page is relatively small compared to its US counterparts [nothing new there then]. But still has a few interesting links, the most interesting I could find on the open access site was this address:
Surplus military equipment:
Disposal Sales Agency,
Seventh Floor, 6 Hercules Road,
London SE1 7DJ
Hey great, maybe they'll have a few spare tanks lying around, I've always wanted one of those for rush hour traffic.
Census Bureau
http://www.census.gov
A BIG site indeed for Population and life styles. You can get maps of every county and major cities in the US.
Central Intelligence Agency [CIA]
http://www.odci.gov/cia
Even the CIA enjoys playing with the Internet, after all, they have been using it for years.
 
If you're into conspiracy theories then stay away from this site, you don't want your email and ISP details tagged [allegedly officer]. Nice sized site with good content.
http://www.tue.nl/europe
A fairly good place to check out before your troops invade. European maps are of a poor quality, but still interesting [just].
DefenseLINK
http://www.dtic.mil/defenselink
Ahha this IS the jump point for information on the US Army, Air Force, Navy/Marine Corps.
FedWorld
http://www.fedworld.gov
The US Federal Governments homepage. An orgy of links to all federal departments and even a job section online so you can infiltrate the governments canteen.
Other not so interesting sites:
http://www2.whitehouse.gov/WH/Welcome.html
No explanations here, take the tour though.
COASTAL WORLD Map's
http://www.coastalcorp.com
Prepare yourself for that difficult beach landing. Not quite as simple as War Craft but just as much fun.
http://www.mit.edu:8001/geo
Excellent site for geographic information about a specific location around the world including population data. Just so you can sneak in unawares.
http://pathfinder.com/travel/maps/
Another great archive of online information. Great zoomable maps and data.
There you go. Please let me know if you do end up invading a country on the basis of the information gained here, so I can get myself a half decent bullet proof vest.