[dvirsky]

Ardour is one of my favorite open source projects, and it's especially admirable considering that it's not a developer and/or server admin tool. It's rare to see people hack away for years on open source desktop software and constantly improving it.

[violinist]

Blender is another excellent example of this.

[pawadu]

Add Inkscape to that list :)

[thomastjeffery]

And Krita

[dvirsky]

And Gimp