Somebody else mentioned the DA 55-300mm, and I agree that would be a nice addition to your lens collection. It will significantly extend your reach, and since the DA L version can be had for a little over $100, it's a relatively painless purchase.
Having 300mm outdoors can be great for shooting sports, nature, etc. But I found that I mostly used mine as a portrait lens. It makes a very nice budget portrait lens due to it's range, decent sharpness, and very, very creamy bokeh. And with the high ISO performance of cameras like the k-x and k-5, it can even be used indoors for fast action (see my Taekwondo picture below). In short, it's a very versatile, easy to carry, high quality lens that you don't have worry about taking an insurance policy out on.
Here are some of the shots from mine over the last year or so: