Again I'm regretting not buying a book on Thai flora on my last trip, but thanks to Google I'm able to at least glean some hints from sites online. Any guesses you'd care to make in the comments section are welcome, as always.
In the second post about Bang Pa-in there was a refreshment trailer beneath a large tree, full of lavender blooms that I'm guessing was a member of the cassia family. A detail of the blooms that hung over that refreshment stand is above. Below is a group of blossoms from a different type of cassia tree - this one being the cassia fistula, or golden shower tree. You'll see these throughout the kingdom.
I can't identify the flowers that hung over the water in the top photo today, either - but here's a closer look at them:
As a final "I don't know" for today's less-than-inspired post, here's a bloom I picked up off of the lawn that afternoon while standing beneath a tree that was absolutely loaded with these yellow ruffled flowers. For some reason I didn't get a photo of the tree itself, but the flowers were beautiful.