This tip saves time with a temporary application of the Ortho command.  I am constantly turning ortho mode on and off.  One day I was using AutoCAD 2008, and while I was holding down the shift key I noticed a little icon next to my cursor. It turns out that while you are holding down the shift key, AutoCAD goes into a temporary ortho mode. Now if I have to draw only a single line using ortho, I just temporarily hold down the shift key. The opposite works also, if you have ortho mode turned on and you hold down the shift key, it will temporarily turn off ortho mode.

NOTES FROM CADALYST TIP PATROL:  Big time saver and one to keep you honest.  Constantly turning ortho on and off is a click that can take up time.  This works just as described.  Draw a line, hold down the shift key, and move the cursor.  This will engage the function, either turning ortho on or turning it off. Tested in AutoCAD 2009