All have suffered mortgage and real estate-related problems and shares in all four rose on Friday in the wake of the Countrywide deal.
Analysts also talked up the possibility of Bear Stearns being involved in a major transaction, despite a statement on Tuesday by its new chief executive, Alan Schwartz, that being acquired is not a strategy for the firm.
A trader of mortgages and mortgage-related investments, Bear took a $1.9 billion write-down in the quarter ended Nov. 30, reflecting the reduced value of subprime mortgage-related securities. Bear Stearns shares also rose on Friday.
"Transactions happen when times are good and valuations are high and they happen when times are very difficult and you have some forced sellers," said Sean Egan, managing director of independent credit-rating firm Egan-Jones Ratings Inc.
"Washington Mutual probably heads up the list (of targets) because they have similar problems to Countrywide," said Egan, adding: "Bear Stearns is an obvious candidate for some sort of transaction."
Spotlight on WaMu
Bank analyst Richard Bove of Punk Ziegel said possible buyers for Washington Mutual could be Wells Fargo and JPMorgan Chase . Bove also believes National City could merge with KeyCorp at some stage.
Regulators and politicians in Washington are very keen to see troubled lenders find solutions to their problems, experts said.
Egan said the Federal Deposit Insurance Corp did not want to deal with the potential failure of Countrywide.
And Bove said: "The people in Washington must be having fits about what would happen if a bank or a thrift with $55 billion in assets went under, so I think they pushed Countrywide hard in this direction."
Markets were hit by renewed concerns over the banking sector Friday after a report claiming Merrill Lynch is expected to suffer $15 billion in lossesstemming from wrecked mortgage investments and UBS said it could not predict the final impactof the subprime crisis.
Bank of America's deal for Countrywideis seen as a move that could help avert one of the biggest collapses in the housing crisis.
For other potential buyers amid the crisis, due diligence has become a major priority.
"I would not be at all surprised to see another half-a-dozen (similar transactions), I would not be at all surprised to see more (subprime) write-downs," said Jim O'Shaughnessy of O'Shaughnessy Asset Management.
"When you look at what will be in my opinion a series of these type of takeovers, you'll see that the acquiring party has obviously done their homework," O'Shaughnessy said.
"They obviously know where the radioactive material is, they'll put their suits on and deal with that and then they'll be able to make use of the good credit that they're buying into."