This tool is designed to let you place spectator cameras in your level with relative ease. It generates a .vmf containing info_observer_point entities configured through this page.
Click "Add Camera" to create a new camera. Then, in-game, position your camera where you'd like your spectator camera to appear, and use the getpos console command to display your current position and angle, and enter the relevant information into the relevant fields.
After you click "Generate .vmf," copy the contents of the textbox below into a blank text file and save it as a .vmf file. You can then open the file in Hammer and use Paste Special to insert the spectator cameras into your map.
Created by Ian "Idolon" Spadin.
Thanks to Sevin for this tutorial.