Ancestral Vision is an example of a card with a total absence of any casting cost: you can't cast it the ordinary way. In this case, you have to cast it using its Suspend ability.
I've just found that I have no idea how to search for these cards in Gatherer or in MagicCards.info. I can search for cards with a mana cost or converted mana cost of 0, but that also gets me cards like Accorder's Shield.
How can I search up cards with no mana cost in either Gatherer or MagicCards.info?
Lands are also in this category — it's fine if this search turns lands up as well; I can exclude those by their type easily enough.