When you get a new Mac, you also get a whole bunch of Apple applications. The General Applications are things you get with the operating system, and if you update the OS, all of them will be updated as well. They are all in your Applications folder. Apple has started giving away the iLife applications with a new computer, but those applications are NOT updated if you simply update the OS. Thus if you had iLife 08 in Leopard and get the Snow Leopard OS disk, it will not update them to iLife 09, you'll still have the older versions in your Applications folder. You'll have to cough up more money to update them. Actually, Apple is offering a bit of a deal if you update to Snow Leopard: you can buy an updater package that Apple is calling the Mac Box Set, and for 170 bucks you get the OS update, plus all of the iLife and iWork applications.
In the Utilities sub-folder of the Applications folder you will find quite a few other free applications, some have a very special purpose, such as the Audio MIDI Setup, or are basically for one time use, such as Migration Assistant, or else they function pretty seamlessly with the Finder or Dock, such as Expose, Grab or Spaces. But several of them are things you might want to use every now and again, or even quite regularly, so I'm listing them here.