We all know that getting a jump on the growing season means starting plants in a greenhouse early each spring.  Why not spread that excitement throughout the year and sow seeds in autumn for an edible winter garden?  Depending on your location November is the perfect time to plant salad crops that will overwinter, providing you with fresh greens into spring.  In mild climates the plants below can be grown outside.  If you happen to be in a place with a little colder temperatures, then growing these in a green house may be necessary.  For optimal results germinate seeds in a greenhouse and move plants outside once they are seedlings.

Collards - Collards are often forgotten as a winter type green, especially on the West coast.  Typically cooked, collards have a strong bitter flavor so use them in limited quantity in fresh salads until you are comfortable with the flavor.  Many of the “bitter greens” as they are called (kales, endive, escarole etc.) are not routinely available in stores and as a result most people are not used to the flavors.  Collards are also easy to grow and easy to overwinter.
Kale - What can I say other than Kale is wonderful!  There are many types of kale with a wide selection of leaf shapes, colors and textures.  Not only does kale taste wonderful, it will add to the beauty of your edible garden.  Kale does very well as an overwintering plant.  In fact, some varieties even become sweeter after a frost.  Most people only like using the young leaves for salad but I find the mature leaves add much needed texture and flavor to most salads.  Mature leaves are also great in soups or baked dishes as they don’t become slimy and fall apart like lettuce or spinach would.
Maché (a.k.a. corn salad, lamb's lettuce) - Maché is an incredibly easy plant to grow.  It was discovered in cornfields where it was thought to be a weed.  This is a low growing plant with very delicate leaves.  The growth pattern of maché is predictable.  Every whorl of leaves are paired and rotated by 90 degrees. Maché to me is similar in flavor to spinach but has a lighter texture.   
Peas - While not a green leafy salad plant, peas, especially snow peas are a wonderful addition to any green salad.  Peas do best in cooler months but are not as tolerant of cold weather as kale or chard so you might find these better suited to growing in a greenhouse.  Nonetheless, peas can be grown for winter harvest.  Peas are a speedily growing plant with harvest between about 55-70 days for most varieties. 
Swiss Chard - Like kale, there are a multitude of varieties of Swiss chard with a range of colors and textures.  Most of the difference in color is in the stalks of chard, some are pure white and others are bright yellow, orange and red.  Again, smaller leaves are better for fresh salads while large leaves and stalks are typically used for cooked dishes, but the choice is yours.     

The amazing thing about all of the above plants is that the harvest can be long, spread out over weeks or months by taking outer leaves first.  In the case of peas, the harvesting will induce production of subsequent pods in most cases.  The next step is to start learning how to grow your own edible garden.