iterm - what's the key-combo to switch panes?
⌘+⌥+←/↑/→/↓ will let you navigate split panes in the direction of the arrow, i.e. when using ⌘+D to split panes vertically, ⌘+⌥+← and ⌘+⌥+→ will let you switch between the panes.

Note: ⌥ is the [alt] key