I'm surprised nobody has mentioned Archangel of Thune. And did anyone mention Felidar Sovereign? Downright brutal, those two cards are.
There's also Blind Obedience, Elixir of Immortality, Blessed Alliance, Exile, and Solemn Offering.
I agree with one of the other commenters (and my best deck by far is a life gain deck) that life gain in and of itself isn't all that valuable unless it's a card that gives you life gain over and over like Staff of the Sun Magus or Soul Net. It's the cards that gain you life and/or trigger an advantage or ability from life gain and do something(s) else that are really nasty.
There's also Blind Obedience, Elixir of Immortality, Blessed Alliance, Exile, and Solemn Offering.
I agree with one of the other commenters (and my best deck by far is a life gain deck) that life gain in and of itself isn't all that valuable unless it's a card that gives you life gain over and over like Staff of the Sun Magus or Soul Net. It's the cards that gain you life and/or trigger an advantage or ability from life gain and do something(s) else that are really nasty.