I tend to the cold side, for the most part, so my summer wear has historically been a nice solid-color cotton T and long pants. The difference is that in summer I wear sandals instead of jeans and running shoes.
However, last summer was spent a few hundred miles south of where I live, and I was finally warm. More than warm, hot. I discovered the joys of cotton or rayon short sleeved or sleeveless blouses, light flowy skirts or cotton shorts, and sandals.
Now that I'm back, I still prefer the button-front cotton blouses (although I've added one or two long-sleeved specimens) and I wear the flowy skirts more than I used to. As I'm somewhat busty, I choose blouses that I need only unbutton the top button to remove, and then I handstitch the button band shut through the critical area, so there's no chance of gaping. I still wear dress pants to work, but I suspect I'll be wearing skirts to work at least once in a while.
I'm fortunate in that I can usually find something that fits me properly - I do a lot of consignment-store and thrift-shopping. I wouldn't know what brands to recommend to anyone, because my wardrobe is a mix of this and that, and it's a minor miracle if I have more than two items of the same brand.