You can chose between chemically competent cells and electrocompetent cells.
Andrew makes chemically competent cells for the lab to use. Several strains are kept in stock in the -80oC freezer.
You can make your own chemically competent cells. From Amada's past mentor in undergrad: For electrocompetent cells, I grow the cells overnight first, then inoculate again in the morning using O/N culture (the volume of new culture depends on how many tubes you want to prepare, let grow for about 3-4 h (OD 0.4-0.6 or so) and then centrifuge and wash 3 times with 10% glycerol (everything on ice). Finally I resuspend the pellet in a small volume (Example, if I do a 5 ml culture I try to resuspend the final pellet in no more than 0.2 or 0.3 ml of 10% glycerol). Then split in 1.5 ml centrifuge tubes (0.1 ml in each), freeze on dry ice-isopropanol and store at -80C.