Hi Donesh!
With Airbus, the last two characters relate to the engines. If the second-last number is 0 it has GE, 1 is CFM, 2 is PW, 3 is IAE, 4 is RR and 6 is Engine Alliance. The last number tells you the thrust rating of the engine on the wing, the higher the number the higher the thrust rating. So A320-232 has IAE engines with a fairly standard thrust rating, the A320-216 that you see with AirAsia and Alitalia (and others no doubt) have CFM with quite a high thrust rating.
With Boeing it's just a customer code. So *38 is Qantas, *FE is Virgin Australia, *36 is BA... there's a list
here (with the usual wikipedia caveat)!
VH-OQK has a 'Spirit of Australians' special livery with people's names on it, as does the B737-838 VH-XZA. The names were chosen through a promotion a while back.
Cheers
Rowan