What Apps should I buy from the Mac AppStore??

Save it and buy something you need when you need it. Different apps are useful/not useful to different people.

A few suggestions...

Well it depends what you want to do. If you want to be creative and try out some HTML5 i strongly suggest downloading Hype, its probably the best mac app i've seen so far.
As an RSS reader, NewsRack is most probably the best option.
If your looking for an app simply to check the weather i recommend 'Weather HD' which has a great UI with some impressive animations.
However, as you own a MBP like myself you probably noticed the speakers are not as powerful as expected, thus 'Boom' is a definite must if your listening to music.
And until OSX Lion is released, you might want to download Sparrow, a pretty intuitive yet compact mail client, much better than apple mail.
There are dozens more paid apps that i can recommend including:
Art Text 2
iMovie
Aperture
StockSpy
DaisyDisk
Angry Birds
& Chopper 2

Enjoy your new mac! 🙂

Buy pixelmator now, it's about to get a big improvement and the price isset to more than double. Early news reports it will be even more improved and potentially a genuine rival to photoshop, which is great as it's already a fantastically polished apple-esque app.

Redeem your card, and buy apps when you will need them, actually.