SLR Lens Review is OK for some ZK lenses:
Reviews
SLR gear has several Pentax lenses reviewed.
Their "blur unit" widgets are quite informative,
although tied to the body they happened to be using:
Lens Reviews - SLRgear.com!
Photozone has some unique reviews,
like for the first three Q lenses,
but the Imatest charts may be misleading.
Also, they are not good at assessing wide-angle lenses,
or telephoto lenses at infinity.
The original Polish version of Lenstip, Optyczne,
has some good critiques of the Photozone tests
(explaining how the two sites
may have widely differing Imatest charts for the same lens/sensor).