in the new L4d authoring tools, valve gives you a plugin for the simple to use 3d cad program by google called sketchup. It works somewhat similar to hammer, but rather then making the brushes in the 2d views, you can edit in 3d space. I might add that it can be used in the orange box and ep1 engine versions of hammer as well.
sample map using sketchup and the ep1 engine-
I wiped this sucker out in 5 min in sketchup, ported it to hammer, put some dev textures on it, so don’t comment on how gay it is.
very useful tutorial-