Lightwright: Absolutely, the most critical piece of software I own. I use this program constantly to keep up with all the paperwork for shows, big and small.
Vectorworks Spotlight: The only drafting program I use; the Spotlight add-on speeds up my drafting functions dramatically.
TrendMicro Anti-Virus: Keeps my machine healthy better than any other program I've used.
eDrawings Viewer 2006: For use when people send me CAD files in DWG format