I have already posted about how you can create customized backgrounds for twitter. Now, here is another wonderful Twitter background designer to customize your profile to make it look more beautiful.

Free Twitter Designer
provides an online Design editor from which either you can choose
existing themes (four are there) to customize or start making new one
from scratch by selecting blank screen.
Editor is embedded with all the necessary tools for designing including Font selection, color selection for various tags.

Just do it as you want - Download the image file - Upload it your Twitter Account from settings - Done!