The following are links to documents discussing Cluster sampling techniques. There is a mix of basic and advanced content. Some documents discuss Two-stage Cluster sampling as well:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2535957/pdf/bullwho00104-0095.pdf

http://www.epicentro.iss.it/okkioallasalute/documenti/letteratura_scientifica/bennet.pdf

http://www.stat.cmu.edu/~fienberg/Stat36-303-03/clustering-rev03.pdf

http://www.ph.ucla.edu/epi/rapidsurveys/RScourse/chap5rapid_2004.pdf

http://cphp.sph.unc.edu/PHRST5/TwoStageSampling.pdf

http://ecology.lifescience.ntu.edu.tw/course_932_ecology/Lab/Two-stageClusterSampling.pdf

http://ocw.jhsph.edu/courses/statmethodsforsamplesurveys/PDFs/Lecture5.pdf

http://www.stat.purdue.edu/~jennings/stat522/notes/topic5.pdf