My mom will get a kick out of this, because she is a huge Harry Potter fan, but I was able to find this picture on the internet of the Sirius Black Family Tree. This took up the whole backdrop, but it sure looks cool with the blue/green background and the white tree winding across the wall.
The photo below is another alternative for a family tree. I found this really interesting website where an artist transforms your family line into art. It isn't a large mural, but she does some beautiful work in watercolor, so if you don't have the space or patience to use up a whole wall for a large piece of canvas, or to paint directly onto the wall, this smaller framed option is a beautiful alternative. You can get this art done at http://www.fmlytree.com/index.php
Check out http://genealogy.about.com/cs/holidays/p/ornament.htm
The example above is of a family tree that I found online awhile ago, and I apoligize for not knowing the source. However, this is also an example of how you can combine your parents family lines. On the left you could have one for your father and on the right your mother. Each leaf would have the name and dates appropriate to your ancestor or living family member.