In a Selesnya populate deck, a card that prevents damage to creature tokens is awesome. Emmara Tandris does just that. Also, populate decks do not try to win on the first couple turns, so she should have time to come out.
Teysa, Envoy of Ghosts
Mana cost-wise, this is a very expensive card for something not very good. Your opponents will be hesitant to attack you however.
Varolz, the Scar-Striped
First, you get to sacrifice a creature and keep Varolz alive, then scavenge that creature to pump him up. Also, the scavenge cost is equal to its mana cost so you should be able to scavenge it.
Vorel of the Hull Clade
For each creature, artifact, and land, you get to double the amount of of counters on them. Think about Primordial Hydra. Because I love math, let's wight an equation # of +1/+1 on Primordial Hydra = x to the power of 4 if you use Vorel's ability.
Tajic, Blade of the Legion
IF YOU DO NOT LIKE BIASED INFORMATION, DO NOT READ THIS (I am addicted to Boros). This card is an awesome 7/7 indestructible. If it were not for the indestructible, I would say this card was OK, but now a Searing Spear of Shock can't kill it. Wizards put my two favorite mechanics into a card from my favorite guild and-bam-awesome card.