what time of year? Don't forget black fly season. Here's a link to NH wedding planning info
http://newhampshire.weddings.com/
DS and DIL were married outdoors in a small public park next to a river but the reception was very casual in the town hall. August is a good month for outdoor weddings.

Our daughter wanted a wedding near the water in southern Maine, nothing too extravagant. We rented the Wells Beach Harbor Park bandshell for the ceremony. This is a spacious park on the harbor, with plenty of parking, restrooms, etc - pretty spot. We had the reception at the Kennebunkport Conservation Trust Clubhouse, a beautiful new post and beam structure located in a rural part of Kennebunkport with lots of privacy. We hired a local caterer (who was fabulous). It worked out wonderfully. There is plenty of lodging nearby, and it's close to the interstate.
Another option is the Lundholm Farm, which is a historic farm complex on a large parcel of protected land on the ocean in Wells Maine - a very beautiful spot. However, this place books up early, and there are a lot of restrictions for wedding receptions.
Of course there are lots of large resort complexes along the coast that do weddings if you want more of a turn key event.

Awesome...I'll check those out.

One issue is we have many elderly folks attending so we need to be careful about terrain and stairs. The flatter, the better. And restrooms need to be easily accessible.

Friends of mine got married at Lynch Park in Beverly a few years ago.

http://www.bevrec.com/lynchpark.html

That was before I knew them, so I was not at the wedding, but their pictures look nice. I have been to Lynch Park, but unfortunately I don't remember anything about the restroom set-up or stairs/terrain.

The Castle at Crane's Beach in Ipswich MA can be rented for weddings. Lovely location.

Back to dfrost's question: when?

September is the best month, May and early June are the worst.

We used to go here when the motel style adjacent rooms were pet friendly. Haven't been there since they renovated, maybe new owner, but the Main House entertainment rooms are historical and lovely and the setting would be wonderful, including other lodging choices just a stroll away.

http://www.oceanviewinnandresort.com/weddings.php

we also went to this inn for a wedding a few years ago, very nice afternoon wedding and then an evening gathering in the downstairs pub. nice atmosphere.

http://www.yorkharborinn.com/weddings/

Wentworth by the Sea

Wequassett

Probably late June...she wants August but my mom says it's too hot.

Went to visit Tupper Manor and she's in love. Not sure my dad's wallet is though.

I know people who have gone to a couple of weddings here and said it was a wonderful place. http://www.elksatbassrocks.com

http://www.wyliecenter.com/weddings.shtml

This is on a lake, very beautiful: http://www.uri.edu/ajc/wpines/amenities-wedding.html

How about York, Maine? The Dockside is on the water, and does weddings. The happy couple can wed outside and go indoors for the reception, and guests can lodge in the inn. Ditto for the York Harbor Inn, and the Stageneck Inn. All serve tasty food, and I believe are reasonable.

My daughter was married at the Dennis Inn on Cape Cod. Very lovely and affordable if you are flexible with dates. All of the non New Englanders loved it and want to return.