The largest and most fun catalog to look through was always the one from the Burpee Seed company.
My grandfather would plan his garden, order the seeds, and plant them in the cold frame he had in a sunny spot on the south side of the house until all danger of frost had passed and the young seedlings could be planted in the garden.
Perhaps one of the oldest mail order seed companies, the Burpee seed company, is still in business. You can request a catalog by mail, or order garden seeds through their online digital seed catalog HERE
Another seed company my grandfather ordered from is now on the internet. He would be AMAZED at this thing called the internet! The Park Seed Company
So, the time to plan a vegetable garden is in late December or early January. If you have never had a summer garden, try not to be too ambitious. Choose your garden location wisely for sun and shade exposure. For your first garden, choose easy to grow plants. If you are successful with your first summer garden, plan to expand the following year. Buy only non-hybrid seeds which will permit you to save the seeds from your garden for next year’s crop.
Not much space for a garden? No problem. Just think small. Check your local library for small space gardening books. Or check Amazon books using the search term Square Foot Gardening. Want to trade all types of seeds with others? Check out the Free Heirloom Seed Swap