This became quite the collection over the years and I thought it would be nice to see them all in one place (tagging all of them was a lot less nice, though).
 
These are somewhat arbitrarily sorted into the following categories (for those interested): Main characters, important secondary characters (antagonists and love interests), female characters already established in MLP, female characters exclusive to Equestria Girls, male characters already established in MLP, male characters exclusive to Equestria Girls, super-powered forms and, lastly, characters that so far haven’t made any appearance in Equestria Girls (to my knowledge).
 

 
Credit for the Tree Hugger design goes to xebck  
Credit for the Wild Fire design goes to MalimarTheMage