If you want to play with just play money then
http://www.pokerrooms.com/ seems to be ok.
If you want to play free-roll tournaments where you can win money then I think a lot of the major sites do them. Not sure what if you have had to have put in money to play them on some sites though. Try Ladbrookes (sorry too lazy to find address), they seem to do a few freerolls according to my housemates, Betfair do one or two every month but you may have to get the passwords.