Anything which does not have controller support. Civ, for example. Lots of other similar strategy titles. They function as a great mouse replacement. I've even used them for first person shooters, where a trackpad in trackball mode can be more accurate for aiming versus a controller.

The right one, that is. The left is more often used for custom menus.

But the fact remains: you are restricted to games with controller support without the touchpads.