One of the first lenses I bought was a Nikkor 50 1.4D. The 50mm seems to be the highest recommended lens for any slr. In fact, many photographers say you have no excuse not to have a 50mm prime if you are a photographer. The 50mm 1.8 runs for a little over $100. For the quality and price, you can’t go wrong!
I was excited to start using my lens, but I was a little disappointed with how soft it was. I bought the more expensive f1.4 so I could shoot wide open in lowlight situations, but the quality wasn’t as good. My depth of field was so shallow that my photos didn’t look sharp at all. I discovered that other people were dealing with the same issues as well. I will say, though, that from f4.0 and smaller the sharpness of the lens is amazing! Below is an example of what I’m talking about.