Right now the Sigma 18-50mm f/2.8 is leading the low light zoom search, with thoughts of a wide & fast prime also being entertained. From post I've read here I see that focal length overlap is good, and that giving up a little on the wide end to gain more on the long end can be good for a utility lens; all of these helping to minimize lens changes.
Pentax SMCP-FA 28-105 f/3.2-4.5 - I can't find much on this lens. At around $200 it looks like a friendlier on the budget than the approx $400 SMCP-FA 24-90 f/3.5-4.5 I've seen recommended here. I think that's what worries me though; what makes the FA 24-90 f/3.5-4.5 cost nearly $200 more than the FA 28-105 f/3.2-4.5? Anyway, I've now got a cross country drive coming up soon, and would like a lens with a bit more range than the 18-55 kit. So, it looks like a good daylight utility lens at a reasonable price would have more immediate utility than the fast zoom. Gotta love how circumstances influence lens desires.