My old favorites for accurate, up to date information on all things military are:
http://www.fas.org/ This is a great reference website with a vast amount of information covering a surprising range of military/government/civil topics. They specialize in nuclear arms monitoring, chemical and biological weapons proliferation, as well as other more esoteric items like mystery aircraft, snooping on classified government projects like HARP, ECHELON, and NMD, and world wide intelligence gathering resources.
Another, more focused/less diverse site is:
http://www.globalsecurity.org/index.html This is a more military-centric, up to date site. I think the information here is presented in a little more user friendly manner, and as for military hadware is much more detailed in general. The most accurate ORBATs would be found here.