I have many times recommended 50mm f/1.8 lenses, and I’ll try to inspire you once more to go out and get one right now. Most manufacturers have a cheap lens like this:
As you will have heard me say many times, this lens is cheap, small, light, fast and sharp.
Ideal for portraits or for low-light subjects or images where you want to dramatically blur the background. If this lens is not in your kit yet, I recommend you add it immediately.
As you will have seen in the previous post, I shot Prof Dawkins yesterday with just sich a lens (my 50mm f/1.4).