...your browser/version number and operating system would sure help..
Assuming you are using Internet Explorer 6 or earlier, then clear the search bar by opening IE, click on "Tools" in the upper left, choose "Internet Options". When that loads, on the "General" tab, then click on the "Clear History" button to clear the web address bar history. Next, click on the "Content" tab, then "Autocomplete" button and choose the "Clear forms" button. (If you're using IE 7, then the "General" tab will have a "Browsing History" section, click on the "Delete" button, then choose "Delete History" and "Delete Forms".)
If you're using Firefox, depending on the version you're running, the search history is contained in the "Tools\Options" section.
Hope this helps.
My EBay search box history is getting very large. Is there a way of deleting the items in the box?