RpR said:Go with decorative concrete retaining wall blocks.
If you can afford to haul in dirt , you can put it on the level with the rest of the yard or you can just raise it as high as you wish.
You HAVE, I repeat HAVE to put a crushed rock base and sand under the wall to avoid future problems.
Also put in a stepped set-back wall with at least two layers so the top blocks cannot be moved by pressure from the dirt over time.