I just tried a search on "retaining walls" and got MANY hits. Looks like lots of good info is out there.
When you said "with either concrete or interlocking mortarless concrete blocks"...
did you mean POURED concrete vs. interlocking blocks, or did you mean regular concrete blocks vs. interlocking blocks?

[This message has been edited by rpxlpx (edited November 01, 2000).]

If you're only going 3 feet high, you can use bricks, block, manufactured 'concrete' blocks, slate, fieldstone, etc.

At that height you don't even need a footer.

You can build a dry wall (without mortar). You need to get some estimates. The local big box (Lowes, Home Depot, etc) will have the concrete products. Look in the yellow pages for a stone supplier.

Prices vary across the country.

I prefer the look of river rock, though I'm building a wall now with fieldstone (free) gotten from area housing developments.