House keys are generally really boring. You can go to your local Walmart and get keys in colors or with designs on them if you want to, but those aren't that interesting to some folks. One of the coolest and most interesting keys for your house that I have ever seen is called the Keybrid. The key has its own key ring integrated into it so you can just clip the key to your keychain or just about anything else.
There is nothing complex about the design of the Keybrid, but it is certainly cool. It's one of those products that you see and wonder why no one else did it before. Right now you can only get the key in plain silver. Next year there will be some new colors added to the line including black, gold, and pink.
The company says that the one key design will fit most of the locks on the market and they even have designs that are made for cars. When you buy, you get a blank key that you take and have cut locally to fit your lock. A single Keybrid sells for $8.99 with the SC1 and KW1 style blank in a package for $16.99.