What adapter do I need for my TV, Display or Projector?

Apple's article http://support.apple.com/kb/HT3235 covers most of the cables needed, except for some Thunderbolt Macs. 

If you have a Thunderbolt Mac, one of the Thunderbolt to HDMI Adapters might be needed for HDMI, one of the Thunderbolt to Dual-Link DVI for Dual-Link DVI (for devices such as Apple's Cinema 30-inch HD Flat Panel Display M9179LL/A), one of the Thunderbolt DVI adapters for regular DVI, and one of the Thunderbolt to VGA adapters needed for VGA.

With pre-2006 Macs, the iBook article from Apple covers iBook adapters. 

The 12" Powerbook article covers those Powerbooks.

For those wishing to connect their AppleTV as a display, this user tip explains what an AppleTV can do, and can't do, and what alternatives exist.

I have no affiliation with Amazon or the distributers selling those adapters,  or knowledge if the links from Amazon are working adapters for your configuration.

Below is an image of the various connectors that Macs can connect to.  

The different display connectors include VGA which has 15 pins, DVI-I which has two groups of 9 pins and a plus shaped connector with 4 pins around it, and dual 
linked DVI which has 25 pins and a horizontal line shaped connector, and HDMI which has a symmetric trapezoid shaped connector that is 2 cm long, and displayport which looks like HDMI except it is flat vertical on one side,
and mini-displayport that is shorter and taller trapezoid than HDMI.