Light green is my favorite color for nurseries at the moment. It's a soothing and stimulating color, and works well for a boy or a girl.
Neutral wall paint in light tones work well as a background for accessories with pops of color.
When in doubt, use lots of white! Just don't forget to add doses of color here and there. Little tykes need visual stimulation.
What a great idea: Hanging vintage children's book illustrations with clothespins. Cute, and very easy to change with time.
Another tactic is to avoid pastels and use more saturated colors similar to this area rug.
Although this looks a little stark for a nursery, the bold stripe of color on the wall and abstract art provide good inspiration.
A blue and orange color palette works well for boys or girls.
Soothing blues and a mix of patterns keeps this room from screaming "baby".