Bricks!!

Bricks - put 'em down in a straight line
Bricks - build 'em into a wall
Bricks - very useful objects
They're not expensive at all

as the Diagram Brothers song went (if I remember correctly).  They were wrong about the last bit - but these are our best compromise of nice hand-made looks without paying stupid money.  Terca Renaissance for the outside and Thermalite for the inside.