Auditors cannot provide other services—mainly tax and IT—to audit clients for auditor independence (SOX in the US, Combined Code in the UK and similar laws are in application worldwide).

All Big4 firms had to shelve their IT consulting to separate divisions or into new companies which most later sold:

Arthur Anderson formed Anderson Consulting which later became Accenture.

Ernst Young - Ernst & Young Consulting which was acquired by Capgemini

PriceWaterhouceCoopers sold to IBM Global Services

Deloitte retained its consulting division I think

KPMG - KPMG Consulting - Bearingpoint?