I guess I want something that looks handwritten. Cursive probably, but it's not a necessity. Something kind of sloppy and just a little bit scary. Something that you might expect to find in the journal of a fledgling serial-killer. Does anyone know of any fonts like this?

It is all a matter of taste. Have a look at 'Themes' > 'Handwriting'.

Or perhaps Horror : http://www.dafont.com/theme.php?cat=110&fpp=50&af=on
Or Brush : http://www.dafont.com/theme.php?cat=604&fpp=50&af=on

Oh! That one worked. "Fountain Pen Frenzy" in the brush section looks pretty perfect. If I manage to actually get something published, it would be okay to use any of the fonts that are Free, right? (Not Free for Personal use but just Free.)

It's freeware.
It means that the author keep the right of this font (so, it's not realy "free") but that you don't have to pay to use it.

Thanks.