You can start by looking to see if your local building office has typical wall detail packets like this one. A landscape designer could typically design the wall for you and advise you if an engineer is needed.

My locally-owned nursery sells quite a variety of formed blocks and cut stone, and the owners of the store can give me quite a bit of how-to information and also referrals. Perhaps you could talk to the people who sell the retaining wall materials and ask them who could design for you?

It will depend on the intended height of the wall and what sort of drainage issues might be involved. In most municipalities, walls in excess of 4' need engineered drawings and permitting approval. Walls under 4' and with normal drainage concerns can be handled by most landscape professionals...doesn't necessarily require an LA.

Thank you all - we are planning for a height of 4'. We will ask at the local nurseries/suppliers that's a good thought.

Yardvaark - yes we'll build in returns, I agree it looks better and makes sense that it would be sturdier as well.