I really don't get why people care so much about what OS someone choses to use to the extent they have to come into this thread and try and make themselves look big and clever by insulting the OP.
Seriously, what does it matter?
It's almost like fervent racism. You all come across like west boro baptists.
Anyway, OP, this is a good place to start:
http://www.allmymacapps.net/
Also, if there is an apple store near you they will run a free series of classes for switchers, explaining the differences.
The first apps I install on a new machine are:
alfred - launcher
transmit - ftp
text expander - removes the need to keep typing the same things over and over