While converting  some of my projects README.txt file to restructured text with vim, I came across the VST package for vim which provides  reST support. After installing VST you can type

:Vst html

or

:Vst pdf 

to generate HTML or PDF from the restructured text document in your current buffer..that's pretty nifty.

With an additional line in your .vimrc configuration file you can configure your own command that converts the buffer to HTML, saves the generates HTML on the filesystem and starts Firefox to preview the file:

.vimrc (LINUX):
:com RP :exec "Vst html" | w! /tmp/test.html | :q | !firefox /tmp/test.html

.vimrc (MacOSX):
:com RP :exec "Vst html" | w! /tmp/test.html | :q | !open /tmp/test.html

and you call the conversion pipeline from vim using new 'RP' command (RestPreview):

:RP