The first six in my top ten are all varieties of Lactuca sativa (lettuce). Growing traditional varieties of lettuce requires no previous experience, the minimum of space and promises delicious leaves and hearts to eat all year round. It is also very easy to save lettuce seed. (link to how to save seed). Different varieties of lettuce can be sown from early spring until late autumn. One of the great secrets about lettuce is that those sown in the autumn and harvested throughout winter and early spring have the best flavour.
The final four are not lettuce in the botanical meaning but in fact varieties of a different species Cichorium intybus (chicory). There are lots of different varieties including root chicory, endive, escarole and radicchio to name a few. My favourites are all sown in summer and autumn to crop through the autumn, winter and into the spring. They provide colour and above all wonderful flavours to winter salads.
Overwintering lettuce and chicories can be grown outside but will benefit from cloche protection. Later sown crops I grow in a polytunnel or cold frame to protect the plants from the ravages of a wet and windy winter.