I started building a white life gain deck. (its on my profile as "HUMAN". I would like to work in Essence Warden and Souls attendant plus I would like to add Ajani's Pridemate. Also if anyone sees cards I have that would perhaps be better suited to the deck any advice would be greatly appreciated. For quick reference the deck as it stands now is as follows: (I would like to keep it Modern, but would be ok if it ends up Standard).
20 Plains
2 Champion of the Parish
3 Doomed Traveler
4 Gideon's Lawkeeper
3 Goldenglow Moth
1 Mikaeus, the Lunarch
3 Ajani's Mantra
2 Blessed Reversal
3 Bonds of Faith
2 Honor of the Pure
2 Revoke Existence
1 Unruly Mob
1 Arrest
1 Gideon's Avenger
2 Oblivion Ring
1 Ajani Goldmane
1 Wall of Reverence
1 Boon Reflection
1 Elspeth Tirel
1 Geist-Honored Monk
2 Landbind Ritual
2 Caged Sun
1 Darien, King of Kjeldor

Its listed on my profile as "Human" as I used my human deck as a starting point. Suggestions for a side board would be helpful as well.

So there are a lot of options for life gain that can work out beautifully for you, BUT, the question is, how much do you want to deviate from your current human-based format? Further, how much were you looking to spend to improve it? For instance, Serra Ascendant is a NICE offensive weapon for a life gain deck, but they come at the cost of almost $4 each.

Some cards to keep your eyes open for include:

Celestial Mantle - it's legal in modern, pumps up your creatures, and lets you DOUBLE your life total if you manage to score a hit with that creature. There are plenty of combos you could run with it to make a creature unblockable if you splash some blue into the deck. Otherwise, think flyers (like the above mentioned Serra Ascendant).

Martyr of Sands - it's legal in modern, is a one drop, and can easily pump your life total if you're running mono-white. Think, first turn you drop it and a land, so you have 5-6 cards in hand. Second turn you draw another card, up to 6-7, assuming you have 2 lands, you can still reveal 4-5 cards and gain 12-15 life.

Elixir of Immortality - I don't really think this needs much explanation.

Chalice of Life - this is legal in standard and modern, is relatively cheap, and when it transforms, is a MONSTER card if the game is stalled (or if you or your opponent has a huge defense).

Beacon of Immortality - pretty self explanatory here. Six mana, double your life, shuffle back into deck, rinse, repeat.

Rhox Faithmender - the pic likely won't work on this one as it's an upcoming card in M13. You can see the specs at http://tappedout.net/mtg-card/Rhox-Faithmender/ - again, doubling life gains whenever possible. If paired with the Beacon, that means multiply your life total by four.

Cradle of Vitality - again legal in modern, and this one goes under the radar from what I've gathered. However, why limit yourself to just Ajani's Pridemate when you can have this enchantment that lets you target ANY of your creatures to give them +1/+1 for EACH life you gain, meaning if you gain 10 life from a Martyr of Sands, pay two, and BAM, your creature of choice gets +10/+10.

Felidar Sovereign - who said you have to actually hit your opponent to win the game? Legal in modern, 4/6 with both vigilance and lifelink. And, y'know, as an added bonus, if you have over 40 life, you win the game in your upkeep.

I hope these suggestions help. White has definitely become the center for IMMENSE life gain. I would suggest keeping some exiling effects in the deck to stop anything that's too big to handle, but realistically, if played correctly, your life gain can outpace the damage they will do to you. One last suggestion would be to include 2x or 3x cards that give one (or more) of your creatures trample, as it sucks to have a 24/24 Ajani's Pridemate that can be easily chump-blocked by a 1/1 token. Here are some equipment that fit the bill (http://deckbox.org/games/mtg/cards?f=27dHJhbXBsZQ**!331!47ZXF1aXBtZW50).

Best luck with it!

I'd say that you should probably not use cards like Gideon's Avenger, it's rarely worth the slot, go for tokens, for example Darien comboed with one soul sister regains any and all life you lose. I would also consider moving to more of flying tokens, because you're lacking in flying defense until late game (A Goldenglow Moth only goes so far) I would say that you're better off focusing on cards like the Soul Sisters (Soul warden + Soul's Attendant) than attackers for the early game, Chalice of life that TyWooOneTime suggested is a phenomenal choice, I would however disagree about Cradle of Vitality, it doesn't come out until fairly late which isn't a big deal since you're going to delay the game alot with this kind of deck. The issue I see with it is just that it's a large mana commitment, I agree that in a vacuum or against non-aggressive decks it's an awesome choice but I'm not sure that I like it in this deck, it's worth trying tho. Also if you do go with tokens Cathars' Crusade is absolutely amazing, that with a geist-honored Monk could easily be a game win. I would focus on ETB triggers from creatures so the Soul Sisters, Suture Priest, and tokens, While I like Gideon's Lawkeeper I'm not sure that it's perfect for this deck, it's worth testing either way.

If you let me know which way you want to go with the deck (One or two huge creatures or alot of tokens or Felidar Sovereign) I might be able to give better advice, I don't want to try to bias you towards tokens just cause I love them, so let us know what you're thinking

Cradle of Vitality is only a large mana commitment if you're looking to add counters from three or four sources across all your creatures at once. It works wonders for creatures with lifelink where you can essentially double the creature's size for only two mana. Cathars' Crusade is a great card, but it only works if you're dropping more and more creatures.

Either way, it's up for however you want to take it Tysonp, but I wouldn't sleep on Cradle of Vitality as it can be a total game changer. But I do agree that if you're going the token route, Cathars' Crusade would be a better fit.

There's also no reason not to do both, a very large creature can block tramplers that tokens couldn't easily block, they're both very good cards and could easily fit, the cradle isn't my personal playstyle but it's still a phenomenal card in a deck where alot of life is gained, if you put in the cradle I would consider Nearheath Pilgrim so you're biggest creature can be the one doubling every turn