There are tons of adorable family trees out there. I have a cute colorable one that looks like a house. I got it when I was 12 or so. It hangs in my living room. I also have a cross stitch pattern for a family tree with a heart carved on the tree and people sitting at the base.
But, now that I'm married I have been thinking about getting something bigger, to include my husbands family. Also, since I've been more into genealogy, I also want something with more information, at least years.
I have found some great ones on Etsy, and even Martha Stewart. The only problem for me is that I have to hand write in the names and information. I don't know about you, but I don't really like my writing, and it's difficult to deal with written mistakes. But, if you are careful and write well, they are great.
For me, I use TreeSeek.com. I like the big 9 generation chart, but you can also do photos, pedigree charts, and even name clouds. And because I use FamilySearch I can just sign in, input the reference number for the person I want to be the base of the tree, and it fill out automatically. If you don't use FamilySearch, you can also upload a gedcom for it to work from.
Another kind of decoration, is to have a literal tree (metal) and photos hanging from it. I've seen them around, in mail-order catalogs and even Macy's.
The newest fun family tree decoration is probably a vinyl wall decal. There are ones with place for picture frames, ones with names, and some that are just trees and a cute genealogy saying.
Whatever your taste, I'm sure there is a family tree decoration that fits your style and can display your family proudly for the world to see.