Basic Numbers, its a CIA (american) based site, which in this case does not represent a problem, as its all raw data:
The True UN, its the official UN site where you can find previous resolutions to base yours upon (take a look around):
UN Charter (dont read it all, just search for specific sections that can be important for your resolution):
For More information of countries, BBC-based, really good:
For topics there is nothing better than the major news sites:
The Economist (more economical, but well written and reliable).
There is also the english version of an individual country`s major newspaper, not all countries might offer this, but its interesting to understand the topic as described by a specific country (Its still hard to find good chinese articles on the 1989 Tiananmen square)
I know all these might seem overwhelming, but its easy to follow all of the recent news on the topics if you use programs like google alerts:
This program will send you an email with all the recent news on anything:
Just be careful with how broad your search topic is, depending on it this might become quite a bother.