If really very very very angry:
ice-cream... works for me !! =) my gf gila ice-cream mar...
Another way... would be to get her something she likes. But for this to work, you gotta be very observant! You gotta really pay close attention to her reaction to everything, everytime u're out with her. There's always certain things that she likes that she's shy to ask u to get for her. So if she's angry, and u pop up with something she really likes... waalllaa !! How can she resist! =) It not only makes her happy getting it, it also shows how much u really pay attention to her... kinda makes her feel loved and all jazz lar...
Last but not least... give her something 'hand-made'. Girls always knows how to appreciate stuff like that... guys usually don't however, so doesn't necessarily work the other way round. HEhehez...
If just a little angry... but feel sorry anywayz...:
Now this is DIFFICULT! Reason being u gotta be creative all the time... as most of the tricks can't be used more than once... here's some tricks
-send her an sms saying "I LOVE YOU" the whooooole message long
-send her an sms noting all the things you like about her
-grab 2 stuffed toys and make them talk to each other... better still act out that they're fighting, den make up
-tell her she wore her shirt backwards, and when she says "no lah, where got?", then u answer, "oh, then its probably just me".. of course you're going to have a figure out a way to get your shirt terbalik first without her noticing lar.
well... figure more out yourself lar... be creative! =) Being sweet, or funny always works. Don't ALWAYS have serious talks to talk your way out of it...