Go Retro with a Beaded Curtain
Take some inspiration from the '60's and '70's, and fill the door frame with a beaded curtain. This doesn't mean your bedroom needs to become the design equivalent of a van with shag carpeting; there are lots of chic, modern options available. Glass, bamboo, and seashell curtains have replaced the plastic beads of the past. A web search will reveal myriad choices. One excellent website is thebeadedcurtain.com, which allows you to search by color, material, shape, style and size.
Keep it Light with Fabric Curtains
An easy, inexpensive option is to hang a fabric curtain in the door frame. Department and home-goods stores stock an extensive range of curtains and the necessary hardware to install them. First, choose a rod that will fit your door frame---anything from simple and no-frills to decorative and opulent. After installing the rod according to the manufacturer's specifications, you can add the curtain of your choice. Try different colors, textures and layers. An added advantage of this choice is that you can change your fabrics as often as you are inspired to.
Choose a Thoroughly Modern Alternative
The Luna Light + Air door is a modern alternative that's getting a lot of attention. At first glance, these contemporary-looking doors appear to simply be adorned with a pattern of small circles. A closer look reveals that these circles can be partially or fully opened to provide ventilation and a view. Dreamed up by a California design group, the door is meant to evoke a state of being "between open and closed." You can learn more on the designer's website: seven02design.com.