Oh Kevin there is so so so much to learn its hard to even think of where to start. Here are some links to some books and top notch instructional videos.

All New Square Foot Gardening
http://www.amazon.com/All-New-Square-Foot-Gardening/dp/1591862027/ref=sr_1_1?ie=UTF8&qid=1302490970&sr=8-1

Garden Way's Joy of Gardening
http://www.amazon.com/Garden-Ways-Gardening-Dick-Raymond/dp/0882663194/ref=sr_1_1?s=books&ie=UTF8&qid=1302491014&sr=1-1

Cornell University's Vegetable Varieties for Gardeners
http://vegvariety.cce.cornell.edu/index.php

Home Vegetable Gardening Part I
http://www.youtube.com/watch?v=_wZes0AnFKA

Home Vegetable Gardening Part II
http://www.youtube.com/watch?v=FYAO5R9_Lsw&feature=channel

Gardening How-To: Pollinating any Squash or Pumpkin
http://www.youtube.com/watch?v=mUB712zzbeM

Starting Tomato Seeds EZ - Home Vegetable Garden
http://www.youtube.com/watch?v=liDKMCFqAGI&feature=channel

This last one is just for the fun of it.
http://www.youtube.com/watch?v=I3DVN7XMiQk&feature=related

I have old books.
1)Step-by-step to Organic Vegetable Growing, by Samuel Ogden
He talks about soil,double dug trench,tile drainage for wet gardens, garden layout & design,composting,garden tools,weeds,insect & disease control.
2)The Ruth Stout NO-WORK GARDEN BOOK, she has a no till garden in 1971. With lots of tips on most of the plants you will grow.
3)Getting the Most from Your Garden, by Rodale Press.
Growing beds,Companion planting,Extending your growing season.Gardening from different Regions
4)Square Foot Gardening by Mel Bartholomew
This is for small gardens, I have over 1000 square feet, but I like the "Outdoor Planting Schedule" it starts 8 weeks before last Spring frost, though 16 weeks after last frost.The chart alone the worth the price of the book.
5)Garden anywhere, by Alys Fowler, she has a earth worm box for worm composting,seed sowing, weeding, harvest & much more.
6)Grow Vegetables by Alan Buckingham, Location, layout,tools,compost,manure,sowing seeds.
Also have a year planner & 8 groups of vegetables, Perennial vegetables-Asparagus,globe, Jerusalem & Chinese artichokes. Herbs is another.
Check out your Public Library 7 used book stores.
GOOD LUCK.

The beauty of gardening is it ISN'T rocket science, despite the likes of EG. Just learn as you grow. Seriously, I know gardeners of 20 years that say they just learned something new. Plant it and if it grows and you like it, grow it again. If not, figure out why and try again.

But to answer your question, leaf lettuce is a good one that you can cut and come again. Just don't take the whole head. Some broccoli's put out side shoots as well. Both are cool weather crops, so if the weather's getting hot there, shade them behind your tomatoes.

That said, yes, I succession plant (plant every few weeks) my salad greens to give me a jump start on the harvest and hopefully stave off bolting in some.

As for books, I think the suggestions above cover most of what I'd consider good.

Enjoy!

Here is a link that might be useful: Sinfonian's garden adventure

Kevin, I think you should have started peppers and eggplants indoors by now. I'm too lazy so I buy my pepper and tomato plants.
I think the original Square Foot gardening book is a great recommendation. I've seen it at used book stores.
You can probably find a website with planting dates. The Old Farmer's Almanac has one which you can customize by your zip code.
Here in NH only my early crops like sugar snap peas and spinach are out of the ground in time for a new vegetable to be planted. I followed spinach (planted April 3 last year and April 10 this year) with carrots, parsley, and Asian greens. I followed sugar snap peas with broccoli in one row and yard long beans in another location. Don't worry, each year you will learn something new. We hope to extend our garden season this year. It seemed like people had to plant spinach, etc by Sept 16 here in NH to have it put in some decent growth before winter but with a low tunnel it can be harvested throughout the winter. You didn't mention bush beans.

I still plant things too close. Mel's book gives great advice for vegetables. Make sure squash and tomatoes get plenty of room.

You might be able to get away with starting tomatoes indoors still at this point, but I do think that defrost49 might be right about the peppers. I usually start peppers indoors mid-March and tomatoes near the end of March. You can always try it and see what happens -- your peppers might just come a little later in the season. If not, you can always buy plants as well!

Succession planting for your carrots, lettuce, and beets is a good plan! You can most likely plant any of those seeds directly outside at this point. Same with chard, though I never succession plant that or lettuce. I use the cut and come again suggestion sinfonian mentioned.

Good luck with everything! :)
Jill

"carrots, beets, chard, lettuce"

I would save these for fall. If I am not mistaken, PA summers are too hot and humid for these crops, even shaded, but once it cools down it the fall they will do much better. It might not be too late for radishes or even small carrots in your area. Check with your local county extension office for tons of info on planting in your region, including what to plant when.

"squash, cucumbers, bell peppers and eggplants... tomatoes"

All great veggies. You don't say what kind of squash, but if it's a winter squash they will easy take over a whole bed. Zucchini and other summer squashes are more compact, but you can't store them for months like the winter squashes. If you like tomatillos, they are not hard to grow as long as you wait until the soil is very warm. And I think a row of pole beans is about as bullet proof as vegetables get -- train it up a trellis on the north side of the bed and it won't take up much room.

I find hot peppers easier than bell peppers, if you are a fan. But with bell peppers $3 each in the grocery store for a ripe red one, I may have to try harder this summer!

Kevin, I have raised beds and also an in ground garden. I like my raised beds for certain crops that don't take up a lot of space like peppers, tomatoes, carrots, lettuce, broccoli, etc. I use my inground garden for vineing plants and corn, potatoes, etc. I enjoy experimenting with different methods and plants and have learned what my family will and will not eat. It's a waste of my time to grow vegetables that my family does not like. Also, have discovered what will can and/or freeze easily. I really like using low tunnel hoops with various shade cloths to prolong my lettuce harvest or warm the soil with black plastic in early spring again useing low hoops with cloth to protect the plants. Above all, relax and enjoy.

To answer your questions:

1) cucumbers, squash, eggplant, peppers. You can still plant the first two, which need to be transferred to the garden fairly quickly, they do not transplant well if they grow too big in the pot. In zone 6 I seed them April 15, you should seed them April 1. Eggplant and peppers, buy plants and seed a few as a test for next year.

2) chard: plant once, it will give you a six months harvest. Seed indoors on March 15 or outside on April 1.

3) lettuce: best not planted in summer. Seed one round now, then seed again in late August-september.

4) carrots and beets: you have time. Plant now or any time until August for fall harvest. Carrots keep getting bigger if you leave them in the ground.

Your lineup needs some filling for the spring (spinach, arugula maybe?) and for the Fall (collard, kale?). The purpose is to have something in the garden from May to December.

A great thing to add right now would be some radishes. They grow very quickly and can be succession planted. They don't do well in the summer but could plant some now and some more in another week. Beets probably wouldn't be too bad either as one can pick them on the smaller side before it gets hot there.

Your lettuces and other greens can be planted fairly close and cut a little bit at a time as baby greens. Clip them off an inch or so above the ground and they'll come back for more harvests.

All of the above advice is fine. However, my suggestion is to "jump in." Sure, you will make a few mistakes. One thing I would say to a beginner - buy seed packets that show the zoning on the back. One of the better reasons for success is to plant seeds according to your particular weather zone.

The reading material that did the most for me was Rodale's Organic Gardening magazines - unfortunately, no longer on the newstands. In my opinion, they were the first publication to introduce the organic way to present day gardeners and gave a lot of us, the inspiration to "dig in and give it a try" so to speak.

I still refer to my old magazines - saved from those early days, when Robert Rodale, Sr., was the editor - his passion for this concept of gardening was apparent in every page.

Just my 2 c's.

Bejay