I don't use them myself as i mainly use betfair but i have an account, they offer prices on 3 or more bookies and you can see the betfair price, at the moment you can't bet in to betfair but they say this will change in the future so you can.

For anyone out there that use the TAB you can bet all 3 tottes at once or select the tote you want, it is a bit like that site http://www.dynamicodds.com/ but on a smaller scale and free to use.