Below is the shelf before.....
I took some MDF (that we had left over from our man cave) and cut them to the size I needed. (Lesson learned: In older houses, don't assume that walls are going to be straight, therefore that the shelves will all be the same length - I learned this the hard way)
I painted all the shelves white, and then gave them a coat of polyurethane.
We had a set of 3 puck lights laying around the house. (We were originally going to have the lights over our TV but decided against it) So I set about installing those on the bottom of new shelves. Of course there were now cords all over the place, so I had to hide them. I had this old round cardboard container in our linen closet, and new that it would work perfect to hide the excess cords.
Then my favorite part, to cover the cords running down behind the shelves, I found some awesome wrapping paper. Now, this wrapping paper was somewhat expensive, $7 per roll, but it was totally worth it. I also had to buy a few foam boards to put the wrapping paper on ($12).
I didn't have enough wrapping paper to cover the very bottom or the very top shelves, which was okay with me, since they also didn't have any lights on them.
Oh yeah, I also put some trim on the fronts of the shelves, to give them more oomph. That was in the scrap section at Home Depot ($1)
So here is the before again, and the after:
Awesome new shelf for $20 - now I just need to fill it.