GM was replaced by Cisco; Citi replaced by Travellers. Source: WSJ. (you may need to get the full article via Google).
Interesing part (for me), quote WSJ:
Why choose a tech company, Cisco, to replace an automaker?
We did not need another consumer goods company after adding Kraft Foods when we removed AIG. In looking around, we were struck by the fact that Cisco makes products that pave the Information Highway – computer networking equipment, things that enable high-speed data and video transmission, and so on. We saw Cisco helping the economy and culture adjust to the digital age, much as automobiles influenced economic and social changes in the 20th Century.
Well, why not Apple (AAPL) or Google (GOOG)?
Those companies certainly qualify as blue chips, but we chose Cisco this time.