Here are a number of data resources.
The CIA World Factbook lists population, government, military, and economic information for nations (especially useful in obtaining data for Taiwan).
Heiner Rindermann calculated Cognitive Ability Sums for 194 countries in 2007. Sum values were available for student assessment studies in 78 countries, altogether there was measured data for 128 countries, with estimated data for 66 countries.
EarthTrends: Searchable Database – Coastal and Marine Ecosystems. A free online database that focuses on issues of sustainable development and the environment. This site draws statistical, graphic, and analytical information from over 40 internationally recognized data sources. Detailed documentation is provided for serious research.
International Futures – Exploring Alternative Global Possibilities. The IFs is a large-scale, long-term, integrated global modeling system that anybody can download for free. It is easy to use, and it is easy to play with the power definition and see the resulting power projections.
Johnston's Archive: Nuclear Weapons provides cumulative estimates for the nuclear stockpiles (warheads and megatonnage) of the United States, the Soviet Union (now Russia), the United Kingdom, France, China, Israel, South Africa, India, Pakistan, and North Korea. And much more…
The Military Balance is the London-based International Institute for Strategic Studies' (IISS) annual assessment of the military capabilities for most countries (that is, those countries that have a military).
The US Energy Information Administration (EIA) provides official energy statistics from the US government as well as detailed international energy information.
The Worldwide Governance Indicators (WGI) project reports aggregate and individual governance indicators for 213 economies over the period 1996−present, for six dimensions of governance:
The Bureau of Arms Control, Verification and Compliance (AVC), US Department of State, releases the World Military Expenditures and Arms Transfers (WMEAT) reports series (updated irregularly), which are designed as a convenient reference on annual military expenditures, arms transfers, armed forces, selected economic data (nominal GDP).