I do as Stitchnripper and Quiltedsunshine do. Place one pin straight up and down through the seams of the two pieces to join. Holding that pin upright/perpendicular to the unit, place pins on either side then remove the center pin. I also (gasp!) sew over pins most of the time. Not quickly, mind you, but it does help to keep everything in place.
Your blocks look extremely well lined up, btw. Doesn't look like you're having much of a problem at all!