I would definitely be pushing these hard - especially if you have decent traffic. I have a list of various football offers (including quite a few acca related ones) here:
http://www.bettingoffers.org.uk/football.html - should save you a bit of leg work :)
There's definitely a lot you can do to the site to ramp up conversions though - as Aidan said, I'd start with more content on the home page. Your sidebar's a bit wasted at the moment - takes up half the page but barely has anything on it. I'd reduce the width (ie: increasing the width of the main page) and add some extra widgets to it such as a latest tips/posts module or a mini table of free bets.
You free bets page (
http://www.footy-tipster.co.uk/free-bets/) needs a bit of love too - try replacing it with an easier to read table, or longer descriptions of the free bets. I would also pad the page out with information about free bets.