In the early days, coffee shops sold mostly imported hashish (cannabis resin). Nowadays Dutch-grown grass dominates most menus (although hash is still available). The famous 'Skunk' originated in America. When it was introduced into the Netherlands, the more relaxed environment and endemic Dutch horticultural skills led to this variety being further improved. Although Holland's climate is not particularly conducive to growing marijuana, the use of artificial lighting for indoor growing has become highly advanced. There are now hundreds of named varieties of seeds available and large-scale cultivation supplies the coffee shops with a good range of exotic herbs.
Growing up to half-a-dozen marijuana plants for home consumption is, effectively, legal. Commercial growing is, however, still illegal so the 'grow rooms' that supply the coffeeshops are still very secretive.
Despite all of the closures and talk of a Wietpas, there are still hundreds of coffeeshops open for business. The vast majority, including all in Amsterdam, also welcome foreign tourists.
This site lists nearly 1400 shops, past and present, with a clear indication of which ones are still open. Check out the Directory for details of all of the shops. The forum is also available as a source of news.