Many Pentaxians (especially those who have migrated recently from ultrazoom p&s) think about of newest (and longest) Tamron 18-250mm F/3.5-6.3 AF Di-II LD Aspherical (IF) Macro ultrazoom lens.
Now there is review at the SLRgear.com:
It competes against other long-zoom designs, both in the form of the original Tamron 18-200mm, as well as the Sigma 18-200mm f/3.5-6.3 and the Nikon 18-200mm f/3.5-5.6 VR (vibration reduction) optic. While it's clear that a $500 ultra-zoom will never compete with higher-priced, lower-ratio zooms, let alone prime lenses, we were pleasantly surprised by how well the Tamron 18-250mm stacked up against the competition.