We have used both CD31 and vWF to stain brain endothelial cells (write me a message if you want to have the datails for specific antibodies). The proteins are generally accepted markers for endothelial cells but do not tell you anything about cell proliferation. On the other hand Ki67 is a marker for profileration but is present in every cell type.
It would depend on the tissues you are staining as vWF is not expressed in all endothelial cell, Article Immunohistochemical Expression of Endothelial Markers CD31, ...
This is a good article comparing a few different markers.