In the Clear Private Data option in Opera, there is a setting to clear history of visited pages. Checking this option would wipe out the entire history including typed in URLs in the address bar. But what if you want to delete only the typed in addresses and not the entire history? Suppose you mistyped a URL in the address bar and it appears every time you click on the drop down arrow.
To remove specific addresses from this drop down list, navigate to your Opera's profile directory. To find out it's location, type opera:about in the address bar and look under the section 'Paths' for Opera directory. The usual location is C:\Documents and Settings\%username%\application data\opera\opera\profile
Now open the file called Opera.dir in Notepad. If you have the extensions for known files hidden, which usually is by default in Windows, you will see the filename only as "Opera". Open the file in Notepad and just delete the entries you wish to remove and save it. DO NOT delete the first line of the file which shows the number of addresses in the file.
The deleted addresses now won't appear in the drop down list and yet your history will remain intact.