I recently published some thoughts on generalization  and included some samples of  generalized coastlines there.  I have now cleaned up the program used for that and make it available as open source.  I also put up a set of files containing  generalized coastlines for the whole earth based on Openstreetmap data for web map zoom levels 1 to 8.

Both are free to use for anyone, the generalization tool under the terms of the GPL, the generalized coastline data under the CC-BY-SA license.  If you find those useful please consider supporting my work using the link on the data download page or by buying a print or comissioning a custom image on services.imagico.de.