I was also looking for such option so I bought the mode
http://www.bcsengineering.com/store/product-sort-by_pro-for-x-cart.html
Above mod has got some nice features to sort the products on category page apart from "sort by date".
But that mods have lots of bugs. I contacted BCSE & they gave me option to deposit $$$ & if the bug will confirmed by their team I will get the refund for the same. This offer does't look valid to me so I contacted the Steve & he removed the bugs for me at the cost of few dollars.
After installing the mod I found 1 more bug. Now it does not display new arrival list on product category page ! Steve is currently very busy with his own projects so I am not able to use this mode even though it's available at very good price.
I guess in the past I found one customization to display newest products first on category page. Please try to search the forum.
I will try to provide you the link of the thread.