There is a free java application available that can convert PC fonts for use with this library. The software is called FontCreator2 and it can produce a header file that can be included in your sketch.
Here is a link to a zip image for FontCreator2: FontCreator2 Zip Image
The font header files created should be placed in the directory named fonts and included in your sketch. For example, if you create a font named myfont in a header named myfont.h then copy myfont.h to the fonts directory and in your sketch:
#include "fonts/myfont.h" // system font
To use the font in your sketch you select the font as follows:
GLCD.SelectFont(myfont); // use myfont
Note that the distribution contains a file named allFonts.h that includes all the distributed fonts, so you can include these files instead of explicitly including the individual fonts
#include "fonts/allFonts.h" // all distributed fonts
In order to make newly created installed fonts “known” by the allFonts.h you will need to not only copy the font header to the fonts directory but also place an include for the font header file in the allFonts.h file.
Font definitions are stored in program memory and this can be significant for larger fonts. The 7 pixel high system font uses under 500 bytes, the supplied Arial14 font uses 1200 bytes of program memory.
Here are some links to additional free fonts that can be downloaded:
Pixel/Bitmap fonts: 1001 Free Fonts
Pixel/Bitmap as well as Dingbat fonts: dafonts
A few tips to keep in mind is that not all the characters have to saved. You can save only a portion or range of the characters. This can be very useful to save memory space if all you need is numbers. Or in some cases fonts may contain characters that can be used as icons or tiny bitmaps. This is particularly true of many of the digbat fonts on the dafonts site.