Originally posted by pepperberry farm gotcha
(cranks up the LBA machine)....
The one to have, without wanting to spend too much money, is the Tokina 19-35 or the 20-35 f/3.5-4.5. I think Andrew_Oid showed how good it is, even at f/4.5. It is rated higher than the f/2.8 models that have the same range. Mine cost me like 90 dollars at KEH and they're usually less than 120. They are especially a good choice, if you think you might upgrade to the K-1 in the future - they are rated higher in overall sharpness (corner to corner) than the Tamron and Sigma 17-35mm models, which go for more money. It does need a hood though, and a regular 77mm hood woks well for APS-C.
The manual focus SMC Pentax-A 24-50mm f/4 is also highly rated. There's an AF version, the Pentax-F but that goes for more than a Pentax 16-45mm f4 so that one, I don't think I'd ever get, it makes no sense since the 16-45 is basically a 22-45mm f4 full frame lens.