What's a zoom tele lens that will give a decent brokeh?

I'm currently using a 55mm-300mm Nikkor zoom and it really isn't a bad lens for as cheap as it is, but the brokeh is very poor in my opinion. I have some otherwise good shots that are tainted by an almost textured looking brokeh. The light fragments are in two parts and it's just a weird looking back ground. Here is an example:

[IMG] http://i.imgur.com/qfqIk.jpg[/IMG]

I'm looking for something buttery smooth, but affordable (is that possible)? Any recommendations? My camera is a D5000.
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Photography is the next best thing to a time machine.