Buses or Busses?

Lately I've been opening up Microsoft Word to correct my horrible spelling while I blog. The squiggley red line is my saving grace. As I was blogging my third post in a row with the word BUS in plural, it occured to me that I was spelling it busses and buses, and the more I switched them back and forth and republished my blog the more confused I got. So I typed in,

there are many buses on this route,
and
there are many busses on this route

And SPELLCHECK didn't correct either one of them!
Now I turned to Google and they use Buses AND Busses....ugh. I'm doomed.