You'd be surprised how often you need to know stuff in a modern game like, "What languages do they speak in Ghana?" or "Who are South Korea's main trading partners?" It's all right there. Quite possibly the most useful thing the federal government provides.
I wish I could share my Jane's subscription with everyone.
If you can pony of the cash, or work for a company/agency that will foot the bill for you it is an invaluable resource.
A more economical (ie Free) recomendation would be the Federation of American Scientists website which has a decent database of world weapon systems in addition to other info.
For those looking for pics/descriptions for a good number of modern firearms "World Guns" is worth taking a look at.