General:
* Yesterday, I...
* You know what?
* Yeah, that's right.
* Yet again, we find ourselves...
* Yonder, across the field, lies...
* You've gotta be kidding me!
* Your presence is greatly appreciated.
* Yield to no one in your pursuit of...
Descriptive:
* Yielding to the wind, the leaves...
* Yonder, where the sun meets the sea...
* Your eyes, like the stars...
* Yodeling across the valley...
* Yonder, a beacon of hope...
Action-Oriented:
* Yank on the door handle.
* Yell for help!
* Yo-ho-ho, and a bottle of rum!
* Yearn for a simpler time.
* Yield to the temptation.
Figurative:
* Your words are like daggers...
* Yonder, on the horizon...
* You're as stubborn as a mule.
* Your laughter is like music to my ears.
Remember, the best sentence starter depends on the context of your writing!