Saw this over at the Valve-Erc forums :
QuoteLike others, I've been frustrated by the limited ability to edit displacements. So I've started on a tool to create displacement curves/bends/arches etc. in a similar manner to the patch meshes of the Q3 engine. Displacements are a lot more powerful as you can edit each vertex independently. The maths was a bit tricky to work out but I've managed to create curved bends so far -
Like it says, it's a third-party tool used to create more exotic shapes with displacement maps. I think it looks very interesting, and I look forward to future versions of it. There's already an early version released, click the link at top to check it out (midway down the thread).