One of my favorite killer-features of Iterm2 is the popup window triggered by a hot-key. It looks like the popups in Quake (the one that would appear once you press ~). It looks like this:
It is absolutely amazing and useful when you need to do something quick in your terminal - for instance, look up some dig output or ping a hostname.
Here's how you configure it:
Create a new profile (or copy the exiting one)
In the Window tab change the Style to Full-Width Top of Screen
(Optional) turn on Transparency and Blur.
Turn on a hotkey. In the Keys tab enable the A hotkey opens a dedicated window with this profile option, then click Configure Hotkey Window and configure the desired hotkey. In my case it's ^I - I don't exactly remember why.
In the same window enable the Floating Window and Animate showing and hiding options. The first one makes the terminal window to popup on top.
Enjoy.