<xsl:template match="/">
  <xsl:copy-of select="html/body/node()"/>
</xsl:template>

An alternative to using copy-of is to use the "identity template", which can look something like this (untested):

<!-- ignore all nodes unless otherwise specified -->
<xsl:template match="node()" priority="0"/>

<xsl:template match="/html/body//@* | /html/body//node()">
  <xsl:copy>
    <xsl:apply-templates select="@*"/>
    <xsl:apply-templates select="node()"/>
  </xsl:copy>
</xsl:template>

You might want to go this route if you ever want to apply other templates to specific elements in the /html/body//* tree. Using xsl:copy-of doesn't allow you to modify the output of the copy with other templates. If you don't think you'll ever need to apply other templates, then copy-of should work fine.