No Deposit Free Bets
There aren't too many of these, unfortunately, but from time to time bookmakers offer what is, in essence, free money in the form of no deposit free bets.
What this means is that, unlike the more common matched bets (stake £20, get £20 free to bet with), these offers are literally no deposit free bets. In other words, you simply register an account and, having done so - without even registering your card details normally - you will be created with the amount of the free bet.
There is currently only one bookmakers offering no deposit free bets, and - obviously - it's worth signing up for.
It is SkyBet, and they are offering £10 free to new customers.