We have this requirement where it states that after performing search user can change how many items are displayed on results page. How one could achieve this in SharePoint 2010? We think about dropdown or static links to choose 10,15,20 etc.
You need to create your own SearchResult web part which inherits from CoreResultsWebPart and assigns the value selected (probably transferred through QueryString in URL) to ResultsPerPage
There is a Results Per Page Search Core Results Web Part on Codeplex which you may be able to use