I've had a go at growing mushrooms in the past using those kits you get in polystyrene boxes and have to put in the shed or the airing cupboard, but they were always for fairly boring white mushrooms.
Recently though, I came across Ardnamushrooms Shitake block at the Partick Farmer's Market in Glasgow in May and they're great.
It's a gypsum and woodchip block that's colonised with shitake spores. You soak it in cold water for a couple of days, then set it up in a humid chamber (basically a plastic box with water in the bottom and an old towel draped through the water and up the sides with cling-film over the top) somewhere it will get the light for at least half the day, and just let it go. It produces mushrooms for a couple of weeks which you harvest as soon as they're big enough. Once it stops producing, you take the block out of the chamber, trim off any bits of mould that have come along for the ride, and store it dry for eight weeks. By then, it's ready for another round of production.
This block is in it's second cycle of production for us and the guy from Ardnamushrooms reckons that it's possible to get up to 8 rounds of production out of one block.
The mushrooms taste really good too!