So that strange ß is called an "esszet" in German, and apparently there's much more too it than I realized. First of all, you can't just go willy-nilly substituting it for any old "ss" you find. It is only appropriate after a long vowel, after a short vowel you just use "ss". For a more detailed explanation, check out this use of esszet in German page. Apparently there was a spelling reform in Germany that attempted to do away with the esszet in 1998 but it hasn't met with much success. And did you know Swiss Germans don't use the esszet? (Hence the reform, to get everyone spelling the same.) More info here.
Where did these crazy characters come from anyway? Origin of the umlaut and eszett. [Note: everywhere I look, people are spelling esszet differently.] I like all the accents and funny characters, I wish English used them. That was one of my favorite things when I started learning foreign languages back in 5th grade: getting to use accents, and upside-down exclamation points. ¡Olé!
Several people kindly wrote in listing other words which contained "ss". One was even so thoughtful to remind me that "ass" has two. I'm certain it wasn't directed at me personally. Thank you dear readers. Thank you.