I've had a few close calls when switching between the Dev/Staging/Prod environments. These will save you from any nasty suprises!
Change the colour of the terminal window when you ssh into your staging or production environments. I use a simple bash script that switches when I ssh into certain hosts.
Banner/Ribbon on Staging/Development
I just used a fork of the Github ribbon
Show App Name and Environment when in console
We used this handy gem Marco-Polo
That looks like this in the console:
~/Sites/myapp$ rails c myapp(dev)>