First off, I would suggest getting rid of the lotus petals and adding in two more lands. 20 is a bit low, even considering your mana generating creatures.
As for creature suggestions, gravecrawler would work very well in a deck like this. If you have the money, vengevine can be worthwhile too. Aside from that, I would just work on getting rid of some of the weaker creatures and getting up to four copies each of the good stuff.