GIMP is usefull tool but default fonts are not sufficient for your creativity but this is not a limiting factory, you can add any opensource font to GIMP very easily.
Download required font from website. one of the best site to get fonts is http://www.dafont.com
Go to Edit–>Preference–>Folders–>Fonts to identify font folder.
You would see two folders
Add fonts to either of folder
Once you have copied font files, re-open the GIMP and your fonts should be available.
Please let me know if you run into any issues.