I'm in the market for a new lens for my Nikon DSLR?

And I want to be able to get a DOF like this:

I only have my kit lens that came with my D3000 and I've read all the book and all the websites but no matter what I do or how hard I try, it never turns out like this. It's too dark, blurry - sometimes it aaalmost there, but not quite…

What lens would you recommend? I'm nervous about laying down a lot of money for a lens that might still disappoint.

Set your aperture to max, maybe f/3.5. Zoom in to 55mm. Get as close to the subject as the camera will focus and you will get the best DOF/blurry background that you can get with that lens. I would shoot Aperture priority and let the camera set the shutter speed. For an outside pic, ISO100 or 200 is fine.