I'm having some luck setting Kindle, EPUB, and HTML fonts in a consistent non-ugly way indirectly using CSS:
<style type="text/css">
p
{
text-indent: 0em;
margin-top: 1em;
margin-bottom: 0em;
}
.fItalic { font-style:italic; }
.fBold { font-weight: bold; }
.fMono { font-family: monospace; }
.fMonoItalic { font-family: monospace; font-style:italic; }
.fMonoBold { font-family: monospace; font-weight: bold; }
.fNormal { }
...
<p class="fMonoBold">This text in Monospace Bold!</p>
Haven't figured out a way to get to the new sans-serif non-monospace fonts in Kindle though ??