Buying a K10

The prices have come down a bit since it came out so I feel I can afford one now.
I think I will try and sell my Isds with it's kit lens. Would that idea make it more saleable?
I will then be left with my 50-200 which I really like and normally keep on the camera.
So what lens would you recommend to fill the gap up to 50mm. I would also consider non Pentax here if the price was right and the quality on a par with the Pentax's.
My preference would be for a Pentax but as Bob Dylan says; money doesn't talk, it shouts or something to that effect.
Many Thanks
Tom

the Pentax DA 16-45 is the obvious choice, you'll probably need to add some to what you get for the DS, but it's a fine standard lens.