Add plants and candles to give a more relaxed feeling to a formal workout space in your home. The gym equipment and TV here lend themselves well to exercise but the candles and plants add a sense of relaxation and meditation that is great for home gyms.
Personally I love the idea of setting up an exercise space so that it looks out onto the yard. This makes it easy to daydream while working out so that you forget what hard work you're doing on the equipment!
A mirror is a great idea in your exercise space. It helps you to see your own form so that you get better and better at your workouts.
Add an inspiring photo to your gym space like the retro fitness posters we see here. This is a fun reminder of what the space is for.
It is important to keep your gym equipment organized regardless of how much or little space you have. The layout here is a great example of good organization. Also consider storage cubbies for smaller weights, yoga mats, etc.
Some people find that large rooms filled with lots of gym equipment are distracting or intimidating. In that case, try a small room with very simple decor and one major piece of gym equipment.
Remember that one great way to workout at home is by swimming. A small lap pool (indoors or out) can be a great investment for the home.
Use large uncluttered floor space in your room for non-machine workouts. Yoga, aerobics, simple stretches and dance can all be enjoyed in a space such as this.