Wow is using NX without a commercial license really that painful? We use it at work amd it's great; much snappier than VNC.
Xpra sounds great but I'm concerned about the lack of support for various features, and -judgung from the FAQ- the author's perception that they're not important.
Yeah, the open-source version of NX isn't really ready to run; it's just a GPL'd library of the core functionality. The FreeNX project produced a working, distributable version (http://freenx.berlios.de/), but it seems to have lost steam--- no releases since 2008. There's also a reimplemented version from Google, though it's not actively developed anymore either: http://code.google.com/p/neatx/