Sometimes you need to decorate your garden the same way you decorate your home.
There are some neat ideas I've used over the 6 year life span of my first real garden. There is nothing stopping you from using items you would decorate your home with and placing them in the garden. For instance, I have a number of candle holders of all shapes and sizes. So I've placed a few of metal ones in my garden to provide visual interest. When guests come over I will even place candles on them lighting the way to our door...
Another great idea is taking broken dishes and pitchers and placing the pieces in the garden. If you have tinier pieces you can press them into the ground and create a mosaic.
Besides using dishes, and candle holders I also like to add traditional garden items. I've also been lucky enough to get pieces from friends who are artists to be a little avante garde. Take this piece from my father-in -law who works with copper. He made this ballerina for me and I've always loved displaying it in the garden close to the walkway up to my house.
Sometimes the best items to decorate your garden, you already own. Make your garden another room you can decorate and you'll have a lot of fun doing it.