I run a blog full of them! www.the-eq-exercise.tumblr.com
Depends on what your goal is. For Suppleness I like to set up a box or + sign. gives me a lot of flexibility to change my patterns without having to change the poles
You can work on transitions between ground poles and also check you control the horse and its straightness. You can also do lateral movements between a kind of lane made of poles.
You should take a look at this article, there is also a quick video http://www.horsechannel.com/english-horse-training/ground-pole-exercises.aspx :)
You can work on transitions with ground poles. On a line, you put 4 poles. You start trotting, after the first pole you canter, then you trot again, and canter again... You can do the same exercises with walk and trot or even walk and canter! Your horse has to be very reactive!
There is one exercise I like to work. You can put 2 or 3 ground poles on a circle and the aim is to keep the same pace in walk, trot or canter. It is harder than it seems! You have to be very regular.