Depends how long I'm planning to ride. Shorter trips I do jeans and t-shirt. Long days I wear yoga pants and a tank or tee. Some day I'll finish my pair of lightweight wool pants and start using those...if I find time and motivation.
I use LDComfort in all weather. In the heat I can get it soaking wet and it will keep my skin dry while it holds the water in and slowly evaporates. It is a bit warm in humid weather, but I'm not sure what works in that kind of wet heat.
I've been looking into some base layers as I currently just wear my normal tee shirts under my jacket. I ordered a pair of Klim solstice 1.0 leggings to try under pants because they were on closeout. Unfortunately the matching shirt on sale was no longer available in my size so I skipped that for next time. I'm fairly resistant to heat, though, so I haven't been miserable yet.