I've heard really good things abotu Alibre's software (http://download.cnet.com/Alibre-Design-Xpress/3000-6677_4-10424841.html). That is the free version. Presumably it will export to DFX.
Will Google Sketchup not export to DFX? ... Looks like it can: http://sketchup.google.com/support/bin/answer.py?hl=en&answer=36203

My experience in using Inkscape for dxf export was very, very bad. It simply didn't work, and when I asked on the Inkscape forum, the answer was that the dxf functionality was non-working and always had been.

Now, that was a version or two ago IIRC, so maybe it's fixed by now. In any case, it's free to try!

Of course the king of the vector format software for digitizers/cutters is Corel Draw.
You can buy the "education edition" of X4 at www.newegg.com for 85.00 and get the rest of the graphics suite as well. The only difference in the ed.v. is you don't get the paper manual. Draw is one of the most intuitive programs I have ever used yet is as powerful as anything on the market. You can use it in freeform or precision drawing mode to create anything from a line drawing to a mechanical drawing with full dimensioning capability, and with > 1000 True Type fonts included that are fully customizable you can design signs and such till the cows come home. I use it to drive my vinyl cutter as well as do sophisticated drawings. Corel Paint runs rings around Photoshop in ease of use and power if you want to edit photos, and Corel trace does a remarkable job of converting raster images into vector drawings.
Highly recommended!

One alert on that: when I used Inkscape to design some engine gaskets and transferred them via eps to Corel, they came out just a hair too small. After some fussing I found out that the error was very consistent, and resizing them in Corel to 107% brought them back to where they needed to be.

YMMV, but check it out.

That education edition of X4 looks inviting.

Hmm, I just realized that my last post looked a helluva lot like the spam we get around here. But no, it was just me.

JC

You may want to check out QCad community edition. It's free and open source. The default file format it uses is AutoCAD's DXF format, but it will only go as far back as r12.

For the plasma cutter, I've had success doing my design work in AutoCAD 2000 and saving as a r12 DXF file at home, going to techshop, loading that DXF into a techshop computer with Solidworks, and exporting back out as a AutoCAD r2.* DXF ascii file.

The only limitation I can think of is that I don't think Qcad (the free version) supports polylines. This means the plasma head will travel up, down, and re-arc for every individual line. You use the "pljoin" command in AutoCAD to fix this; There's probably a way to join the lines in solidworks but I'm not sure how to do it.

Anyways, QCad is free and AutoCAD-like, but you'd still need to use solidworks @ techshop to convert it.

I just installed CMS XPandy. It has a Save As file type: "AutoCAD Release 2.6 ASCII (dxf)" (among many other file types).

Corel Draw file export lists Autocad (.DFX) but doesn't specify version #.
My vinyl cutter has a Draw plugin that allows me to cut directly from within CD. Is there possibly a CD plugin for the plasma cutter available since CD has taken over from AI as the defacto standard vector drawing program for sign making etc.?

Something new I have started using is Draft Sight.

http://www.3ds.com/products/draftsight/draftsight-overview/

It is a free 2d CAD program made by the same makers of Solidworks. Nearly identical to Autocad in every way. If you did not know it was Draft sight you would swear it was the latest version of Autocad. Check it out.