Even a small amount of recursion can go a long way toward turning a good deck into a great one, and it can be achieved with very little effort
Tree of Perdition $15.90 Tree of Perdition is a cool design, and one that has jumped quite a lot over the last year or so due to a newish deck coming out of Pioneer
At the minimum six mana you can either draw three cards, have an opponent discard three cards, or give your creatures +3/+0, trample, and haste until end of turn
Of course, the Black Lotus has reached the millions in value in private sales, but those are also typically graded copies that have been well preserved for years.
Again, I dont hate every double-faced card (cards with strong stories like Delver of Secrets and Thing in the Ice are pretty cool), but they introduce a lot of complexity and make drafting a huge pain, so I tend to avoid them altogether in my cube designs