Don't get so involved with planning, landscaping and growing your garden that you forget that gardening is a form of self-expression. Stop thinking about impressing your guests or caring for your plants for a moment and consider the sorts of cool garden ideas that really show who you are. Realizing your ideas and working them out is what makes your garden great.
Most collections are kept inside to protect them from the elements, but some collections fit into an outdoor garden. Display collections of bottles, geodes or other interesting rocks, shells or farming antique outside in your garden. Place small artifacts on outdoor shelves, tack them up on walls or even place them in flower beds. Use larger items such as farming antiques as decorative features to give your garden character.
If you have a flat, accessible roof, build a roof garden to help you enjoy the view. Roof gardens insulate in both the summer and winter, and protect roofs from weathering from ultraviolet light and frost. Create a container garden as a starter project. Growing plants in containers will require no modification of your existing roof structures. Alternately, build an extensive roof garden. Install a waterproof layer, such as asphalt. Cover that layer with a roof membrane, such as a pond liner to protect from plant roots. Add a thin filter sheet and a commercial moisture blanket which will retain water to nourish your plants. Install a sedum mat for drainage and a thin layer of soil, and you're ready to begin planting!
Using candles is an inexpensive and classy way to add ambiance to your outdoor environment. Collect Moroccan lanterns, Santos candles, paper or cloth lanterns and scatter them about your garden---creating a wondrous disarray of firelight for romantic evenings, nighttime reading or communing with nature after dusk.
The shoe planter is a recycling classic that will definitely make a statement in any garden. Fill an old shoe with well-drained soil, taking care to fill both the heal and the toe. Put small plants or small plant seed in the soil, and water as you normally would. Soon, your old shoe will burst with new life.