Everybody who knows anything about Unix loves cowsay. It's quaint, it's fun, it's got interesting history.
Throw in a random phrase, a selection of alternate cowfiles, maybe some rainbow colors, and you've got a nice greeting for starting a terminal!
What you might not know is that the humble cowsay has a graphical sister program. xcowsay! Also many years old, but a little less flexible and a little less interesting. A similar genre to xeyes. If you're on Arch, you can find it in the AUR under 'xcowsay'. IIRC Debian has it under the same, and thus also Ubuntu and its derivatives.
I have a lot of fondness for xcowsay. If you too are fond of silly little x applications, I recommend adding a background call (&) to xcowsay or xcowfortune to your .xinitrc/DE startup script/whatever you have tied to logging in and starting X. It's fun!