I had the same problem myself once with very tiny fonts that I needed a magnifying glass to read
The kde fonts are easy to set but it was the gtk apps that I had a problem with.
For gkrellm, you can change them by going into the configuration and under themes, click on the fonts tab.
Not sure about the other apps unless they also allow you to set them in their configurations, and it's been a while since I had the problem but I believe I had to create a .gtkrc and .gtkrc-2.0 file in my home directory, a little googling brought me to
http://voxx.demon.co.uk/linux/linuxd...00050.txt#0022
and under the section `Setting gtk and gtk2 default font sizes' sounds like what I had to to do. Hope that helps