As primarily a Windows admin (Yes, we exist on Lemmy ;) ) here are few I use often.
Enter-PSSesion
Get-ADUser (also group and computer)
CLS (aka the superior clear)
ii . (short for Invoke-Item . which runs the selected object using the default method. For paths (like .) the default is explorer, so ii . opens the current directory using explorer.)
ft (short for Format-Table formats piped input as a table.)
fl (short for format-like. Used like ft but for lists.)