Although I post some information about splash screens, I'm not a huge user of 'eye candy'. I can tell you that there are about 10 standard Grub2 splash images available in the repositories.
You can install them via command line:
Once you run the code, they can be found in /usr/share/images/grub/
sudo apt-get install grub2-splashimages
If you find one you like, you can either copy/move it to /boot/grub, where it will be added as a background automatically (in Natty), or use this setting in /etc/default/grub:
Don't forget to run "sudo update-grub" to add the change to grub.cfg
(There is also a link in my signature line for Grub Customizer installation and usage).