I'm fed up with giving any more money to Murdoch, so I'm cancelling my Sky sub too. If you want to keep the sky box, as l45key said, you need to pay £25 for a viewing card that allows you to watch free-to-air channels: http://www.freesatfromsky.co.uk/faqs-freesat.aspx#q3
If you want to keep the Sky+ functionality, you'll need to pay Sky £10 a month.
Alternatively, keep the dish and wires, ditch the box and get a Freesat box from Humax that does all the same stuff. http://www.freesat.co.uk/
I'm looking at replacing my Sky+HD box with the Humax HD PVR that's £200-250. Plugs straight in, does the same stuff and will pay for itself in about a year.