NOAA is now providing both raster (RNC) and vector (ENC) charts at no cost.

RNCs

ENCs

Comparison of raster versus vector charts

Stay clear of proprietary format chart such as those offered by Garmin, Nobeltec, Navionics. As not only are they quite costly, they will only work on one registered Mac and updates are not free.

MacENC works with both type of free charts.

Create your own BSB Marine Charts (RNCs)