A sky box without a valid card will receive all 'Free to air' channels, which are marked as 'FTA' in the list here:
http://www.wickonline.com/fta.htm
Basically, that's the same line-up as conventional analogue TV (BBC1, etc), plus some foreign language stations and lots of radio stations. It doesn't include many channels from the Freeview line-up. All Free to Air channels are unencrypted.
The satellite equivalent of FreeView is FreeSat. The range of channels available is similarto , but not identical to, those on Freview. FreeSat channels aren't 'Free to Air'. They're 'Free to View'. This means that they're encrypted but don't require a subscription to view them. However, you do need a valid card in your Sky box. This is a special FreeSat card, which can be purchased for a one-off payment of �20 from Sky.
Information about FreeSat is here:
http://www.freesatfromsky.co.uk/
That link states that FreeSat costs �150 but that's only for customers who don't already have a satellite dish and box. The reference to the �20 card can be found, here, among the FAQs:
http://www.freesatfromsky.co.uk/?pID=6
Chris