Smaller dithers- Giant Danios: they are very fast and with proper care can have nice color and reproduce. I have even had success keeping them with md-lg cichlids in bigger groups.
Large dithers- Tin Foil Barbs and Gold Tin Foil Barbs: love these guys first off...they grow very fast, can take quite a beating, and from my experience even can dish one out(they have no problem turning and taking on some of my md cichlids or atleast reminding them that they are tough too). Always my choice for larger cichlids!
I know and have seen alot of people using Silver Dollars(never personaly tried them) and they always seem to be beat up or very shy/timid so again TFB for the win.