Alright so I installed one of the maps, and my crosshair went away. I had this problem once before in Portal and was able to go into the console and type in crosshair 1 and it would go back on. However, I just tried to do it in Portal 2, and my crosshair is still gone and is no longer showing up in any of the maps. Does anyone know how I can turn it back on?

This thread on the Steam Forums says to try:

cl_drawhud 1
crosshair 1
hud_quickinfo 1

It's a thread about Portal 1, but the commands are probably the same.

Make sure you actually press the Quit button before exiting Portal after you execute those commands in the console so it saves to your config. Otherwise your crosshair will keep disappearing.