Categories and CategoriesSB
 

Deffinately a couple of apps worth checking out.
Categories makes it so you can group all your apps into different (get this) categories :)
CategoriesSB integrates them into the SpringBoard, so they load up faster and anything you have in the different categories will be able to be found in the search. Also with CategoriesSB, if you make a category called "recent" it will have all recently opened apps.

Like I said they both are nifty and deffinately worth checking out at least.