Hi,
I really like emc2 (free) which runs on Ubuntu Linux (free).
www.linuxcnc.org
I still have NCPlot2 (Windows) to convert DXF files to gcode as well as VCarve (Windows) but I have created a couple of starter files for my router and my lathe that allow me to program most parts by hand with only a few lines of gcode having to be written.
You can also get QCAD to run on Linux, Mac or Windows. It is available as a free demo and a licensed copy is only 35-40 dollars. And there is a program ACE converter that is free to convert DXF to gcode (I have never used it).
Alan