Interesting shots!
For #2, watch the angle of straight objects, I do the same thing, it is very hard. For the 40D, you can actually buy the EF-D grid focus screen, and it gives you horizontal and vertical lines, as well as 1/3rds, it makes a huge difference for me in composition.
For pic #3, something I want to try is getting a neutral density filter, set the camera on a tripod and do a longer exposure in the sun on a waterfall for a cool shot, making the water flow more of an ethereal look. Something to consider in the future, if these areas are readily accessible and you can take them anytime you want.