Tonight I figured out a synergy that is absolutely crazy, but I haven't seen anyone else mention it. Anyway, without further ado:

Find steed is fantastic on its own, but what makes it truly amazing is one line hidden in the middle of the text. "While mounted, you can make any spell you cast that targets only you also target your steed."

Now take a second look at, for example, two of your third level spells, aura of vitality and spirit guardians (if you're oath of the crown, or multiclassing). Both target... only you. They affect other creatures, but they are a radius with a target of self. Now they also target your steed (specific trumps general; the range of self is overruled). So if you're letting your mount act independently rather than treating it as a controlled mount (which you should be doing anyway with find steed) your mount can contribute its bonus action and you are healing 4d6 HP per turn as a bonus action for a full minute or as long as you maintain concentration. Or, with spirit guardians, you're dealing 6d8 (+2d8 per spell slot level above 3rd) to every hostile within 15 ft.

Ladies, gentlemen, and anyone else: that is crazy good.