Does anybody know which IT consulting firm pays it consultant the most? What percentage of bill rate do they pay?

Bain has leaped back to the top of its game. The firm is ranked among the world’s most prestigious consultants, along with McKinsey and the Boston Consulting Group — which once employed founder William Bain. Bain is rare among major consulting firms for having a woman, Chairman of the Board, Orit Gadiesh, at the top. The firm employs 5.000 consultants.
Equal in prestige to its close competitors, Bain has a smaller, more congenial feel than larger rivals and views encouraging a friendly environment as a worthwhile expense. Among special touches is the “Bain Band,” an amateur assembly of Bain employee-musicians who serenade fellow “Bainies” at company events. Insiders say pay is generous and raises average more than 15% a year.

depends on a lot of circumstances: they may be the highest paying firm out there, but if you don't have any credentials or experience, don't dream about getting the top-dogs paycheck.
you want to earn the highest amount you can get? then don't look for what they can offer you, make sure YOU have something you can offer them. expertise, for instance, pays up.

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Thanks for the input. Does anybody have experience with a firm who pays well and takes care of of their consultants?

re-posting "anyone" now and then won't land you better or more answers.
you want to get well paid? make sure they have an actual reason to pay you well. as I said before: this doesn't only depend on what firm you work for, it mostly depend on what knowledge and experience you add to the overall knowledge and experience of the firm and its co-workers.

make sure you have a good overall knowledge, specialize if you want, and apply for several jobs. that way you can find out who pays the best for you at this moment.