master.xml

<data>
  <results handle="results" value="results">
      <item>
        <artistname handle="artistname" value="artistName">Radiohead</artistname>
        <collectionname handle="collectionname" value="collectionName">The Best of Radiohead</collectionname>
        <trackname handle="trackname" value="trackName">Karma Police</trackname>
      </item>
      <item>
        <artistname handle="artistname" value="artistName">Radiohead</artistname>
        <collectionname handle="collectionname" value="collectionName">OK Computer</collectionname>
        <trackname handle="trackname" value="trackName">Karma Police</trackname>
      </item>
      <item>
        <artistname handle="artistname" value="artistName">Radiohead</artistname>
        <collectionname handle="collectionname" value="collectionName">OK Computer (Collector's Edition)</collectionname>
        <trackname handle="trackname" value="trackName">Karma Police</trackname>
      </item>
      <item>
        <artistname handle="artistname" value="artistName">Radiohead</artistname>
        <collectionname handle="collectionname" value="collectionName">OK Computer (Collector's Edition)</collectionname>
        <trackname handle="trackname" value="trackName">Creep</trackname>
      </item>
 </results>
</data>

master.xsl

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">

  <xsl:output method="xml" indent="yes" />

  <xsl:template match="/">
    <ul>
      <xsl:for-each select="data/results/item[not(artistname=preceding-sibling::item/artistname) or not(trackname=preceding-sibling::item/trackname)]">
        <li>
          <xsl:value-of select="artistname"/> - <xsl:value-of select="trackname"/> 
        </li>
      </xsl:for-each>
    </ul>
    <ul>
      <xsl:apply-templates select="data/results/item" />
    </ul>
  </xsl:template>

  <xsl:template match="/data/results/item">
    <li>
      <xsl:value-of select="artistname"/> - <xsl:value-of select="trackname"/>
    </li>
  </xsl:template>
</xsl:stylesheet>