Okay, Sam. I have the D80 with the 18-135mm/3.5-5.6 lens. What will the 50mm 1.4 do for me besides set me back as much as a good scanner?

Keep in mind, my main subject is a VERY active 4 year old and I don't have the best indoor natural light in my home.
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Cassie
My Gear: Nikon D300s w/18-200mm VR & 50mm 1.4
Software: Adobe Photoshop CS4, PSE 9, Lightroom 2