AlertNet has a list of contact numbers for aid agencies working in Colombia.

The BBC country profile includes profiles of armed groups.

The Centre for Research and Popular Education (Centro de investigaciones y Educacion Popular CINEP) is a think tank which tracks human rights violations. Its website, in Spanish, includes a round-up of the latest news and reports from rural areas.

The Colombian government's Presidential Human Rights Programme compiles data on kidnappings, murders and massacres. It's in Spanish, but its statistics lists are fairly easy to navigate even with rudimentary vocabulary.

Colombian think tank Fundacion Seguridad y Democracia - Security and Democracy Foundation - in Spanish, compiles data on urban safety levels, as well as deaths in combat, and looks at trends through the last two presidents' terms in office.

The Internal Displacement Monitoring Centre collates displacement estimates from a range of sources, and publishes its own analytical reports.

Belgian think tank International Crisis Group offers in-depth reports on the demobilisation process and the role of drugs in the conflict.

The U.S.-based Center for International Policy runs a Colombia blog which is openly sceptical about U.S. policy, but picks up on some interesting trends, and links to official statements as a good counterbalance.

The U.N. refugee agency, UNHCR, detailed its estimates of the numbers of people needing help around Colombia in its 2008-2009 funding appeal, and the agency has a page on Colombia.

U.N. Office for the Coordination of Humanitarian Affairs offers a plethora of reports, maps and links to organisations working in Colombia, in Spanish.

The U.N. Office on Drugs and Crime regularly reports on trends in coca cultivation in the Andes.

It's a bit hard to find relevant information on the website of the U.S. Office of national Drug Control Policy but if you dig deep you can find the official U.S. line on the efficiency of aerial coca crop eradication, and estimates of drug harvests and the size of South American lands being used for cultivation.

And here's a book: "Inside Colombia: Drugs, Democracy and War" by Grace Livingstone, 2004