I'm in Zone 5, about 20 miles north of Boston and I'm looking for pretty
tree suggestions -- maybe something w/some type of berry on it (aren't
there
trees that have berries in the winter?). Something that will attract
different birds or interest the ones I already have even more. The
front
yard will look so empty w/o a tree in it, I need to replace it
w/something.
Also need to give the birds good cover and a safe place to go to from the
bird feeder that's already in the front yard.

LeeAnne -- Why not replace one with an Oak and the other with a flowering
tree like a Crab Apple? It will be many years before another oak reaches
the same size as the ones you're removing of course so size will not be an
issue and you'll keep the nut food source for local wildlife. A Crab Apple
is small, gives a nice flower show mid to late spring, and the apples will
be a fav for early returning birds. Cherry is another nice one for flowers
and bird food. If you REALLY want to make 'em happy, plant a Mulberry
tree -- our birds absolutely adore the ones we have and so do the dogs (it's
the only part of the yard that is strictly off-limits for, ahem, relief).

If you really want to give the birds a food source and shelter/safe place,
you might want to consider some shrubs. Our birds love the shrubs as much
as the trees for quick getaways at the bird feeder. (Although, there are
just as many in the trees -- they all sit up there and tweet at me to get
out of the way so they can get back to eating!) Shrubs tend to produce a
lot more berries for birds than you'll get out of trees.

James