What alternatives are there to a retaining wall?
You really have two primary options--slope or no (minimal) slope. 

With the no-slope option you need either a single retaining wall or multiple tiers of landscaping. You could use small boulders to create two or three individual levels and fill between with gardens of various sorts. 

With the sloped option you need to prevent erosion, so sod or a stable covering is needed. Crushed rock or paving stones might work.