Opera

For Opera 9.62:

<package id="opera" name="Opera 9.62" revision="962" reboot="false" priority="1000">
 <check type="file" condition="versionequalto" path="%PROGRAMFILES%\Opera\Opera.exe" value="9.62.10467.0"  />
 <install cmd='"%SOFTWARE%\opera\Opera_962_int_Setup.exe" /S /V"/qn CREATE_DESKTOP_ICON=1 CREATE_QUICKLAUNCH_ICON=0 CREATE_STARTMENU_ICONS=1 MULTI_USER_SETTING=1 INSTALLER_LANGUAGE=en"' />
 <upgrade cmd='"%SOFTWARE%\opera\Opera_962_int_Setup.exe" /S /V"/qn CREATE_DESKTOP_ICON=1 CREATE_QUICKLAUNCH_ICON=0 CREATE_STARTMENU_ICONS=1 MULTI_USER_SETTING=1 INSTALLER_LANGUAGE=en"' />
 <!-- FIXME remove cmd='???' -->
</package>

This is a silent installer and uninstaller for Opera 8.

<package id="opera" name="Opera (WWW browser)" revision="1" priority="0" reboot="false">
 <check type="uninstall" condition="exists" path="Opera" />
 <install cmd='%SOFTWARE%\opera\ow32enen802.exe /s' />
 <remove cmd="%PROGRAMFILES%\Opera\UnInst\UNWISE.EXE %PROGRAMFILES%\Opera\UnInst\Install.log" />
</package>

You can also unpack the installer (i.e. with 7-Zip) and install the MSI directly. (no luck with this with 9.6)

msiexec /qn /i "%WPKG_INSTALLERS%\opera\Opera installer.msi" INSTALLDIR=%ProgramFiles%\Opera9