Install Steam – quite a few games on it for Mac these days.
Big Aperture fan here for photo wrangling. iPhoto is very good too though if needs are more basic.
+1 on pixelmator or recent mac Gimp builds are getting a lot better if you prefer free ( don’t require X any more, far more native http://gimp.lisanet.de/Website/Download.html )
Safari for browser preference, works much slicker and lower power use IME (though I’m chrome all the way on my win/nix boxes).
MOBAC if you’re after offline mapping etc.
I’m pretty into the combo of notational velocity + simplenote account + various phones.
+1 on superduper for keeping a bootable backup (in addition to timemachine).
iTunes is fine.
TBH quicktime plays most stuff I want to. VLC for when it doesn’t.
Look at how you use full screen apps and spaces (4 finger swipe between them). Miss this a lot on other OS when working on just a laptop screen.