I was given the
Young's Microbrewery for my birthday last year, which I recommend. It took me a while to start using it, but I've done three brews with it in the last two months.
It comes with all the basic kit you need to get started, including a two-can extract kit (it's advertised with a Woodforde's Wherry kit but mine came with a St Peter's Ruby Red Ale kit). You just empty the contents of the two cans into the fermenting vessel, add water, add the sachet of yeast, leave it to brew for about a week, then rack it off into the pressure barrel, leave to condition for a couple of weeks, then start drinking. And I must say that the results are pretty good.
If you want to bottle your beer instead, you obviously need to provide the bottles (I've just collected a load over the months rather than putting them in the recycling), as well as a capper (about £10-£15) and some crown caps (about £3 for a bag of 100). It's also a good idea to get a bottling wand (a syphon tube with a valve in the end) and a bottle drying rack.
Obviously that set comes with an extract kit to get you started, but further kits are readily available - one-can kits are cheaper (£10-£15) but need you to add a bag of sugar to make up the fermentables and the resulting beer will have less body than an all-extract kit. Two-can kits cost around £20-25 but don't need anything added and tend to give better results (according to what I've read, rather than personal experience). Of course, you can use dried malt extract instead of sugar in the one-can kits, but then you're ending up not really making a saving on the cost of the kit. Tesco Direct have some pretty good deals on kits - when they're in stock, which isn't often. Wilkos also stock a good range and have some good offers.