When I modify WWG graphics for kitbashing, I use Adobe Acrobat to convert the PDF to JPG. Of course, not everyone has access to $200 software.

What do you guys use?

I would assume that GIMP has a similar option and is free. Like you, I personally use more expensive software myself.

I got a couple year old version of Photoshop for my wife a couple years ago.
She uses it most of the time for her digital photo editing.

But when I do have time, I do almost all my work in that. It really is wonderful once you learn how to use it. (and I only know the very basics, theres a TON of tools in there that I just haven't learned yet.)

So Photoshop will take PDFs and convert them to JPG?

You can import PDF straight to photoshop and then save down to JPG if you like. You can also simply cut and paste from a PDF document into a new photoshop document.

or have too pdf to image converter
also have too PDF-XChange Viewer

Blender is really powerful for 3D modelling. GIMP I have less experience with, but have heard good things about it. There is a hack of GIMP called GIMPshop which puts all the buttons in the same place as photoshop and tries to make the interface as similar as possible to that of photoshop, so if you're used to photoshop you can use GIMPshop fairly easily.