Is there a database containing sequences of human cell lines?
As pointed out by @kmm (http://cancer.sanger.ac.uk/cancergenome/projects/cell_lines/) is an excellent database. Alternatively you can look at the broad institute page (http://www.broadinstitute.org/software/cprg/?q=data-resource) in the cancer cell line encyclopedia section, then go to the browse tab and select the cell line for a very comprehensive list of cell lines.