Of course, in the category of Live Performance (Non Grateful Dead), the best segue of all time is Thin Lizzy's "Cowboy Song" > "Boys Are Back in Town"
This tweet is brought to you by The Pretty Things' "Parachute," specifically the transition between "Good Mr. Square" and "She Was Tall, She Was High," which may be the best segue this side of the "Abbey Road" medley