A good explanation of why Greece needs more money just to pay maturing debts. But the money won't be cheap as Greece's borrowing costs are already sky high - the yield on 10 year bonds is about 17%.
Default is being discussed, but for euro-zone banks that are holding Greek debt, that would be a disaster - further amplified by holders of Credit Default Swaps who would promptly demand payment on their contracts.
The bottom line is that Greece is probably too big to fail. But it may be politically impossible for Euro zone politicians to convince their electorate that a bailout is the better of two very bad options.