The tutorial on the LWJGL wiki explains how to use the Slick-Util TrueTypeFont class very well. However, when I started using the class, I found it's been marked as deprecated. What's the recommended way of dealing with fonts?

Yes true, I've already raised a bug report on the slick forums about this issue here. Slick2D has a lot more options for fonts, including TrueTypeFonts, UnicodeFonts and AngleCodeFonts (BitmapFonts) so hopefully the author of Slick-Util will fix this soon.

Yeah, I've messed around with Slick a bit. None of those options are in Slick-Util?

no only TrueTypeFonts, but they could easily be added, you should post on the linked post above to request the features you want, the author is usually pretty good at adding RFE's.