You can add a History tab on the Personal bar by typing in 'Opera:History' into the address box then bookmarking the resulting page on your personal bar. You can also add a History button to the Personal bar by editing the 'toolbar.ini' file in the main Opera folder (C:\Program Files\Opera). Just add the lines below:
[History Panel Toolbar]
Button0, "View Complete History"="Go to page, "opera:history""