Often I will just "wordlessly" think to myself that I like what I see. If mental words are expressed, it's usually something along the lines of "nice."
There are rarely any subsequent thoughts or actions. I often note when I see someone I find physically attractive, but in the vast majority of cases, I will leave it at that, as I will probably never see her again. Those I find really, really attractive are people I have some kind of relation to, so that I get to know their personality. That's where the subsequent thoughts and/or actions come in. But even then there are rarely any subsequent actions, and thoughts center around how attractive she is.