The following links are to sites/ documents providing insights into sample size calculation, with special emphasis on the notion of Design Effect. Some discuss sample size calculation in greater detail than design effect, and vice versa:

http://www.ph.ucla.edu/epi/rapidsurveys/RScourse/disasters30(2)199_211_2006.pdf

http://www.amstat.org/sections/srms/proceedings/y2001/Proceed/00144.pdf

http://biostat.mc.vanderbilt.edu/wiki/pub/Main/TheresaScott/SampleSize.TAScott.handout.pdf

http://timss.bc.edu/timss1995i/TIMSSPDF/TR2chap5.pdf

http://faculty.smu.edu/slstokes/stat6380/deff%20doc.pdf

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1705515/pdf/11524_2006_Article_9106.pdf

http://dental.usm.my/ver2/images/stories/AOS/Vol_1/09_14_ayub.pdf

http://www.stats.ox.ac.uk/~snijders/PowerSampleSizeMultilevel.pdf

http://en.wikipedia.org/wiki/Design_effect