So here's (most of) the process for that latest piece.
About 3 1/2 hours or so, took sort of longer than usual 'cause I fugged around a bit to begin with (not really captured here).
Photoshop CS4, full res is about 4700px wide.
All done with the square brush found here
Final is here
(it's a big file, so might take a bit to load; hit download if it's not working, hopefully that should help)