Hi Crystal,
If you have the room you could use evergreen trees. They would provide privacy, greenery in the winter, and a nice background for the Maples.
Norway Spruce take up a lot of room but are very nice. If you have just a small space, consider a hybrid of the American Holly, Nellie Stevens or Foster Holly. They stay quite narrow and do not get all that tall.
Whether you plant the trees on the street side or the house side depends on the room you have and also which view is more important. For example, if they are placed on the street side, you will view the nice Maples up against the evergreens from your house. This would be my choice.
