I loved the exploration and settlement allowed in Kingmaker. I also enjoyed the settlement stuff from the GMG. What other products expand on these two areas?
None that I know of from Paizo, to date.
Jon Brazer Enterprises has been reproducing the rules material from Kingmaker as stand-alone products in their "Book of the River Nations" line. The latest volume is the first to add significant new material in the form of feats, spells, and other player crunch.
Kingmaker is/was popular enough that Paizo has said they will probably (but no definite promises) do something to expand the rules for kingdoms in a future rulebook.
There are some alternate rules (esp. for building alternatives to farms, like mines) in a thread in the Kingmaker forum.