Free plants by propagation from cuttings and slips

If you like a particular plant and want to ensure you have more of them for next year then propagation by cutting is the easiest way to go, and best of it costs nothing. 
Not every plant can be propagated successfully but there are some annuals, biennials and a lot of perennials which should root easily enough.
There are various ways of propagating new plants, either through seed sowing, root division or taking cuttings. The latter is the least labour intensive and usually nets the quickest results.