Well, here in the Pacific Northwest, where I live, one might argue that we lack well-defined seasons and from October through May suffer from near-constant, chilly rain. And yet I have the same outfit for the entire year. I just think in terms of a clothing continuum.
I should think the same would work for you in New England, where there ARE well-defined seasons (hot and humid summers; nice falls; freaking freezing cold winters, usually; and sweet springs).
Heres the system. Start with a set of light long underwear such as Patagonia Capilene 1 T and Bottoms ($36 each; www.patagonia.com), and add the Ex-Officio Amphi Short ($46; www.exofficio.com). Then youll need a set of midweight long underwear. I like Icebreakers merino wool stuff, such as the Skin 200 Mondo Zip T ($69; www.icebreaker.com) and Bodyfit 260 Leggings (also $69). Add a soft shell top such as REIs One Jacket ($199; www.rei.com) or a fleece piece such as L.L. Beans Mountain Pile Fleece Jacket ($69; www.llbean.com). Over it all, use a waterproof-breathable shell set, such as Marmots Tamarack Jacket ($200; www.marmot.com) and Light Streak Pants ($225). Add some gloves and a hat, and maybe a super-warm insulating piece such as The North Face Nuptse down jacket ($199; www.thenorthface.com), and theres nothing you cant endure.
The beauty of it is, you can start with the light layer and just keeping adding stuff over it from August through February, then start peeling it off. Or mix and match. Capilene 1 and the One Jacket. Icebreaker Mondo Zip and Mountain Pile Jacket. Capilene 1 and Mondo Zip and Pile Jacket and Tamarack Jacket. And so on. You can fine-tune your comfort level in five-degree increments from 90F to minus 20F.
So, thats the system. Hopefully you already have comparable versions of some or all of the pieces, or this will get kind of expensive. Remember, you dont need to buy all this stuff at once, and shop around for the best deals.
Check out this years more than 400 must-have gear items, including a comprehensive apparel section, in the 2006 Buyers Guide.