I originally designed levels for my yet-to-be-released iPhone game by coding the layout by hand using a calculator and pen+paper. I switched to Inkscape to do

I originally designed levels for my yet-to-be-released iPhone game by coding the layout by hand using a calculator and pen+paper. I switched to Inkscape to do level design and then finally spent a couple of hours banging out a crude designer in html + javascript. That was a major productivity boost.