Having searched the Magento help libraries and videos extensively to find some advice, I finally found a great solution to changing the number of columns of products that are displayed in a Magento category or search result (and therefore how many products your customer can see on a page).
There are plenty of suggestions that involve hacking the core code (not a great idea if you're planning on updating the installation), rewriting template files and several other methods. Then I came across this elegant and simple solution. Just by adding one line to one file in within your Magento template you can change how many products are displayed.
<?php $_productCollection=$this->getLoadedProductCollection(); $_helper = $this->helper('catalog/output'); $this->setData('column_count',5); <------ add this line ?>