I like the roles as defined but I'd include a few more varieties;
Support Not individually powerful but acts as a force multiplier on allies, and allows allies to keep going longer than they otherwise would. Cleric, Bard, any other buffer
Spiker A class with a limited usage of very powerful abilities that allows him to contribute more to any single given encounter, but as a consequence less to all the rest. Spellcasters, Psions, Barbarians (assuming he can only rage a limited number of times)
Support Not individually powerful but acts as a force multiplier on allies, and allows allies to keep going longer than they otherwise would. Cleric, Bard, any other buffer
Spiker A class with a limited usage of very powerful abilities that allows him to contribute more to any single given encounter, but as a consequence less to all the rest. Spellcasters, Psions, Barbarians (assuming he can only rage a limited number of times)