Hello,
congratulatiosn to your K10D!
Let me just quote, what I suggested to another member recently in the following thread (sometimes questions are very similar, so that often the search functions does wonders

)
What lens on a K10D? :
'I had the
Pentax 16-45 and sold it after 2 weeks for two reasons:
1. The zoom range was too small for me
2. In wide angle it is too long to use the internal flash (gives a shodow on the bottom)
Instead I bought a
Sigma 17-70 (F2.8-4.5), which does not have these two problems. What I read in various forums about it was very good. Some think it has the same quality as the 16-45 (F4), others think it is very close to it. I did not see any differences in the image quality and I like it very much.
Furthermore it has a macro (1:2:3 20cm), which I enjoy, and is (a little) cheaper (appr. $ 350).
If you are looking for a definitely better quality, maybe
primes (no zoom) could be useful. There are the so called limiteds from Pentax (DA series is new, FA series almost not available anymore). This is a question of style and budget to my opinion.
If you are looking for a very very easy to use lens and you do not want to change lenses, the new
Tamron 18-250 (F3.5-6.3) could be of interest to you. (I think it will be available as of March or so). But it should be clear, that even though quality of big-range-zooms improved very much over the last years, you will not get pictures like the ones from roy. I expect it to cost appr. $ 500.
An in-between-solution could be the
Sigma 18-125 (F3.5-5.6), if you do not need high mm for long distance. It is very important that you check the quality of it, because there was a significant variance of quality reported in the forums. But it could be that this is solved with the new edition (to be identified: logo is not only printed, but has a structure). It costs appr. $ 350.
(All prices are estimations for US, because I live in Germany.)
Maybe I could help you a little in finding a decision. In case of doubt, stick to your 18-55 for some time.'
Have fun with your K10D,
Jacob