My favourite from the former: Maximilien Luce's Notre Dame, Paris, View from the Quai Saint-Michel 1901-04

The evening colours and purple shadows here just knocked me flat. In person, this work is huge, too... This probably goes for everything in this thread, but the full effect in person doesn't really come across that well in a photograph on a screen; in this case, not least because it's a pointilist painting. The way it all melds together is...! My gosh.
My favourite from the latter: Arthur Segal's The Port

I can't form any words at all for this one. Are you seeing this...?