Bet365 gives new customers a 100% first deposit bonus up to £200 in free bets.

All new customers can now receive free bonus bets worth up to £200.
Simply register, deposit (a minimum of £10) and get your deposit amount doubled with a bonus of up to £200.

Upon registration Bet365 will send you an offer code that you enter in your account within 7 days after your deposit.
You can use your bonus money once you have turned over your deposit once. Afterwards, the deposit and the bonus have to be turned over 3 times (at minimum odds of 1.50) before making a withdrawal within 90 days.

Don't worry it sounds more difficult than it is.
Please see full details at Bet365.