Battlerager x2? j/k
There are numerous options really. But a defender and a leader is the most straight forward solution. A guardian fighter and a battle cleric would be an excellent duo, and fairly straight forward to get used to and play.
However the players shouldn't feel restricted to these roles. Two strikers, say a Ranger and a Rogue, can work in a slightly non-traditional way as a pair of assassins. You would just have to line up the adventures to suit them a bit.
A Paladin and a Barbarian could be another interesting option, both with some self rejuvenating powers, good healing surges, and with the Barbarian filling in the Striker role.
A dwarf in the party would be a good thing, because they can use second wind as a minor action, and that's exceptionally useful in small parties.