There are likely many such charts for outdoor plantings and frost dates, but to say when seeds should be sown indoors, that takes some planning.

I can give dates when I start them in zone 5b and you are likely a few days later in the Hudson Valley.

I start broccoli and cousins inside on about March 18th...with heat for a quick germination and set them out while small about April 13th.

Tomatoes I start about the 29th of March for May 10th set out. Peppers can be started then or a few days later. Peppers are very slow to germinate compared to other veggie seeds.

I take them outdoors a lot to toughen them in.

When I Google 'seed starting schedule' all sorts of them pop up. Linked to one below. You'll also finds links to others in the discussions over on the Growing from Seed forum here. Lastly, check your county extension website as most of them offer some form of guidelines on the issue for your specific area.

Dave

Here is a link that might be useful: Seed Starting schedule

These books are great
Getting the Most from Your Garden by Organic Gardening Magazine, this is a good one with a chapter & chart on starting seeds.
But the best is: Square Foot Gardening by Mel Bartholomew. It is the best because it has a chart from 8 week before last Spring Frost to weeks after Fall Frost.
This is listed by crop.

Also - keep in mind any micro-climate or climate modification you intend.

For example - if you have a very protected site with a wall/fence to the north, you can likely plant out a week or two early than in an open area, and thus can start your seeds earlier as well.

If you are using any row covering - even just the bug barrier for the brassicas, that will give you some slight protection and you can plant a week early.

Johnny's Selected Seeds has a seed starting calculator on their website. You enter your last frost date for the year, and it calculates dates to start inside and when to plant out.

Here is a link that might be useful: Seed Starting Calculator

The back of seed packets give you starting times.

One thing to remember, the temperature inside is very important. My house is very cold, can get into the 40s downstairs where my seedlings are, so I start my tomatoes 10-12 weeks before I plan on setting them out. 10-12 weeks in a normal 68 degree house and you'll have 4 foot tall plants.

Thank you all so much! Very helpful.

harryvetch - Do the tomatoes do well at that temp over time? I've heard below 50 is verboten?