Cont...
As for the pay sites...
http://www.ancestry.co.uk/ - Has all English and Welsh censuses (1841 - 1901) and some Scottish ones. Has complete BMD index 1837-2006, WWI Army Service Records, some historic nespapers and much much more.
http://www.findmypast.com/home.jsp - Similar to Ancestry in what it offers. I don't know exactly as people tend to use one or the other and I use the other!
http://www.genesreconnected.co.uk - DON'T SIGN UP FOR THE GOLD MEMBERSHIP. That offers credit to search census etc etc. The credits are expensive copmpared to other sites, are a complete waste of money and only direct you to the other sites anyway, just pay the �9.95 for 6 months to allow you access to the message boards where you can ask questions and get help. You can also build your family tree on there and lots more. Just don't pay for credits...
http://www.familyhistoryonline.co.uk - quite a useful site, you can buy �5 worth of credits which last for ages. No census info but they have the NBI (national burial index) and some other records that can't be found on other sites.
As I said, you can do your tree for free offline if you are prepared to travel. To do it online you WILL need to pay for information, genealogy is not a cheap hobby but is very rewarding!
You will still need to visit Records Offices at somepoint anyway as pre-1837, records available online become few and far between!