Last Two Centers
There are many more cases than what is listed here, as these are only ones that I feel are worth noting.
A good systematic approach to the last two centers is to create a 2x3 block on one of the centers, then finish off the last 1x3 block (The first 18 cases below will cover this).
I do not recommend memorizing any algorithms for this, but rather develop a good visual on how the pieces are being manipulated to solve each case. They are very intuitive and can easily be applied at numerous angles, and even during the first four centers.