Neil,
There are many good places to bird in Massachusetts. Here is a site that provides a lot of information:
http://www.massbird.org/
I also recommend getting a book called "A Birder's Guide to Eastern Massachusetts" which describes numerous places to bird and what you are likely to see. It is available from the American Birding Association if you cannot find it locally:
http://americanbirding.org/Merchant2/merchant.mv?Screen=PROD&Store_Code=ASBS&Product_Code=266
At that time of year, the most interesting birding is for shorebirds (called waders on your side of the pond), which are migrating south, terns and pelagic (open ocean) birds. The two best spots for shorebirds and terns are South Beach in Chatham on Cape Cod:
http://home.comcast.net/~odenews/SouthBeach.htm
and Parker River National Wildlife Refuge, aka Plum Island, near the northeastern corner of the state:
http://birdingamerica.com/Massachusetts/plum_island.htm
http://www.parkerriver.org/
For pelagic birding, Wilson's Storm-Petrel (and sometimes shearwaters) can often be seen from land at South Beach, Race Point in Provincetown on Cape Cod, Eastern Point in Gloucester and Andrew's Point in Rockport, the latter two north of Boston. All are described in the book and the site listed below. Your chances of seeing pelagic birds is even better if you get out on a whale watch boat, which operate from several locations in the state, including Boston. Even if you don't see any pelagic birds, seeing the whales is worthwhile. Local birding clubs have a couple of outings on whale watches scheduled during late July-early August. You are welcome to go even if you are not a member. Having other birders on board can be helpful if you are not familiar with pelagic birds -- shearwaters can be a little tricky at first and the naturalist working on the boat usually focus their attention on the whales. Lots of info about pelagic birding, including scheduled club trips, can be found here:
http://www.neseabirds.com/
Birding for land birds is not particularly interesting at that time of year, but if this is your first visit to the area, you should be able to find many of the more common resident species and summer breeders that would be new birds for you. In Boston itself, try the Arnold Arboretum and the Boston Nature Center.
http://www.arboretum.harvard.edu/visitors/visitors.html
http://www.massaudubon.org/Nature_Connection/Sanctuaries/Boston/index.php
Mt. Auburn Cemetery in nearby Watertown is more famous as a spring migration location, but it has many of the common residents in summer.
http://www.mountauburn.org/
All of these are accessible by public transportation. If you have a car and can get out of the city, there are many, many possibilities.
Re field guides, I agree with streatham's recommendations.
Good birding.
Glen