There are a lot of ideas on inflatable Christmas lawn decorations at Inflatible Season. There are good prices on each unique outdoors display. There is a funny one about an elf flatten by Santa, seven feet tall for $99.99!
You should check your local yellow pages for places that will rent inflatable decorations for Christmas. I couldn't find a location for the type of decoration you need but it doesn't mean they are not around. Check with your neighbors as well, they might have some great ideas.
You can find ideas and instructions for handcrafted Christmas decorations on this site (http://familyfun.go.com/christmas/christmas-decorations/christmas-ornaments/). You can make anything from homemade paper stars to candy cane signposts.
Some sites to find Christmas ideas for decorating are allthingschristmas.com and diynetwork.com. They give decor ideas and tell you where you can purchase them.
You can find unique Christmas decorations and ornaments at http://www.squidoo.com/christmas-tree-themes. There are also gothic Christmas trees and decorations. Try http://www.squidoo.com/GothicChristmas
You can find personalized Christmas decorations at several websites. Squiddo.com has a variety of Halloween themed Christmas decorations for you "dark tree". Or, you can try searching for ideas to create your own homemade decorations.
You can find unique ideas for Christmas window decorations at http://www.bhg.com/christmas/decorating/christmas-window-decorating-ideas. You can also find windows displays at http://shop.christmascentral.com/Xmas%20Lawn%20n%20Window%20Decor/Window_Decorations/ and http://www.christmascentral.com/content/pages/christmas-window-displays
You can find origami Chrisrmas decorations. You can find origami Christmas decorations at www.origami-resource-center.com/christmas-ornaments.html. These Christmas decorations are not too hard to make.
I like shopping at Kmart, Target, and Walmart for outdoor Christmas decorations. However, their stock may not be out yet. Check their online counterparts or Amazon for some ideas.
Inflatable holiday decorations can be found at WalMart. WalMart is a store that sells many items online. You can purchase decorations from WalMart and they will have it delivered to the store for free or to your home for a nominal cost.
I'd highly recommend checking Youtube on how to reuse some of your Halloween decorations for Christmas. They usually have some great ideas and would also be able to help you learn how to make your own to add your own personal touch.
You can easily find different photo Christmas decorations online. I would check amazon.com for example and search for items like Christmas cookie cutters or Christmas decorations.
Browsing images of Christmas decorations is a great way to come up with ideas for your own designs. Some great places to look are http://www.fotosearch.com/photos-images/christmas-decorations.html and http://www.bhg.com/christmas/indoor-decorating/your-best-photos-christmas-decorations--2010/.