Here is a guid to install a very nice plymouth theme made by DanoDyMake. One of the nice things is that the startup and shutdown screens are different... To install the DM-Ubuntu Plymouth theme follow the instructions.

Download DM-Ubuntu Plymouth theme Here. When dowloaded double click on the dm_ubuntu_plymouth_theme_by_danodymake-d2zzae5.2.zip file and extract the content to your desktop. Open a Terminal window (Applications -> Accessories -> Terminal) and copy+paste the following lines:

cd Desktop

sudo cp -R DM_Ubuntu/ /lib/plymouth/themes/

sudo update-alternatives --install /lib/plymouth/themes/default.plymouth default.plymouth /lib/plymouth/themes/DM_Ubuntu/DM_Ubuntu.plymouth 100

To sellect the theme:

sudo update-alternatives --config default.plymouth

A menu will apear. Type the number that corresponds to DM-Ubuntu in the list and press Return. In your Terminal window Copy+paste the following line:

sudo update-initramfs -u

To see the DM-Ubuntu plymouth theme in action restart your computer