This summer, I went with my friend to the Penthouse Bar on top of the Reina Victoria. It was a Monday night, and although we were not dressed like supermodels, we got in easily. There wasn't a cover charge (I don't know if there normally is or not) and it wasn't crowded at all. I suspect that since it was a weeknight in the summer we were able to enter with no problems, but perhaps you could try a similar tactic while you're there. We only had one drink while we were up there (and the drinks weren't cheap, but they certainly weren't the most expensive ones I've had either in Spain or the U.S.), but it is a gorgeous view of Plaza Santa Ana. It would be nice to see it during the day, too, so you could discern the buildings a little better.
As for the Corte Inglés on Gran Vía, I was on the top floor cafeteria for the first time this summer, too. I had no idea that the place even existed and then what a neat view there was up there.
There was a thread about this topic earlier this summer, so go
here to read more and to see links to photos from other threads.
Hope you find some great views, and let us know where you end up!