PCB Plugins (more detail coming eventually):
Autocrop()which shrink-wraps your PCB down to just the existing elements. Read the original announcement.
SmartDisperse()which improves on
DisperseElements()by using the netlist as a hint. Read the original announcement.
Align()which can evenly space or align elements using a variety of reference points. Read the original announcement which includes many examples or another message with tips.
Everyone has a boxsym script. Mine is the result of starting to hack on
djboxsym and then deciding to rewrite it. It's not finished, but there are
some really good bits. Most interesting is probably the pseudo-PostScript
gaf package that lets you render symbol primitives with
translation, rotation and mirroring. Eventually all boxsyms could be
written as layout modules for this program.
If you're considering gEDA/PCB, here are some sample projects I've done using the tools: