HeLa cells are certainly the most famous. It should be noted that the HeLa stocks used in most labs now are radically different from original HeLa stocks.
Even in routine experiments, you have to keep a bunch of cells frozen in liquid nitrogen to replenish your "working stock" of cells. After around 30-40 passages (e.g. generations of cells), most immortalized cell lines start to get funky with mutations and exhibit different behaviors. You kill them off and go back to your frozen stocks to get back to the "original" genetics.
Nobody patented "a human cell". What can get patented is the method for creating this cell line. Here's the classic (and controversial, but for different reasons) patent related to the Mo cell line (T-lymphoblasts):
These are cells from a person, Henrietta Lacks, which can be grown in a dish and which keep dividing, for ever.