Well that's a big question. You don't say what your yard is like in terms of size and/or whether you need shrubs, trees, perennials, or flowers. I suggest you go to our Plant Encyclopedia on this Website and do an Advanced Search.
Plug in your criteria, and it should help you by giving a planting list. Since you have several sides you want to landscape, you probably should do a separate search for each side, depending on the amount of sunlight each area receives. You can also look at the plans in our Garden Plans section of the Website to get ideas. There are more than 200 plans there, so you'll probably find some that fit the shape and size.