Borromini's S. Carlino (or San Carlo alle Quattro Fontane if you want to be technical)
Santa Maria in Cosmedin - it's not visible in this particular photo, but the timber trusses looked amazing.
S. Maria del Popolo
Incredible ... S. Maria del Popolo
S. Maria degli Angeli e dei Martiri (tepidarium of the Baths of Diocletian)
S. Maria degli Angeli e dei Martiri - look at the scale of it! It's enormous, but actually not overwhelming at all. Quite fantastic.