After the soprano thread, let's turn to the mezzos. Here we have the opportunity to appreciate both the babe roles and the sensitive (or not so sensitive) gent roles that mezzos can switch between. Think of one that you really love from each category (or either, if you only like one or the other). In the interest of avoiding arguments over the definition of mezzo arias, you can also include castrato arias that have routinely been sung by mezzos as well as countertenors and whoever else who has the range for them.
I'll start:
femme fatale: Mon coeur s'ouvre a ta voix - the definition of sultry, hot and cold at the same time and completely mesmerising
furious young man: La tremenda ultrice spada - Romeo spits expletives to a jaunty tune - what's not to love?!