I often like to change the background from light to dark or vice-versa depending on my environment. I use the Solarized theme and it comes with two lovely variants, light and dark.

I used to do this by manually entering:

:set background=light

But why do that when it’s easy to set up a mapping to toggle them automatically for you:

map <Leader>bg :let &background = ( &background == "dark"? "light" : "dark" )<CR>

Now it’s a simple case of ,bg (I have my leader set to ,) to toggle the background.