LibreCAD is another free/open source/donation possibility.  

LibreCAD is a free Open Source personal CAD application for Windows, Macintosh and Linux. Support and documentation is free from our large, dedicated community of users, contributors and developers. You, too, can also get involved!

It is another variation on QCad.

How it started

LibreCAD started as a project to build CAM capabilities into the community version of QCad for use with a Mechmate CNC router.

Since QCad CE was built around the outdated Qt3 library, it had to be ported to Qt4 before additional enhancements. This gave rise to CADuntu.

The project was known as CADuntu only for a couple of months before the community decided that the name was inappropriate. After some discussion within the community and research on existing names, CADuntu was renamed to LibreCAD.

OK, just downloaded and compiled...
Looks pretty snazzy (QT4 and the green icons are a breath of fresh air)
2 of my pet peeves about this program are still there:
1- No American paper sizes listed in Document Preferences or the Print dialog (yes, there is a "Custom" size, but seriously...).
2- In "Print Preview" the scaling options are listed as inches to inches, when it should include inches to feet (e.g. 1 inch = 10 feet)
The most common architectural scale (in the US, anyways) for normal house plans is 1 inch = 4 feet, but that ratio isn't in the menu, so I have to enter it manually.

Pros:
LibreCAD has a "Custom" size listed in the print dialog, QCAD doesn't.
Now I can finally make 36" x 24" PDF's that are in scale.
That's almost a deal-maker right there...

Cons:
Can't figure out how to change the icons.
Minor annoyance, but I wonder how long those green icons are going to seem "cute".

Bugs:
In LibreCAD's print preview, the scale box is empty until you click it, then it shows the menu.
After entering in my standard 1" = 48", it resizes the preview correctly, but the box goes blank again.
I'm sure that's a VERY minor issue that's going to take a few keystrokes to fix, but it's a bug nonetheless.

Overall, I've got good feelings about LibreCAD, I think I'll keep it...

Thanks for the tip, Bob99!!  

EDIT: I just found the PNG files for the icons.
Prolly easy enough to make the colors into something a bit more subtle, but it would be better to give the option to change them from within the application rather than have to re-compile.