Just like you would transfer ANY data from an old Mac to a new Mac. Run Migration Assistant. In fact, it'll run automatically when you first start up the new Mac (it will ask you if you want to transfer files from an older Mac).
If you miss that step, run it from the Utilities folder. You can migrate files with an ethernet cable (recommended, it's fastest), Firewire (you would need a Thunderbolt-Firewire adaptor) or wirelessly (generally much slower).
iTunes: How to move your music to a new computer:
This is our resident iPhoto guru, Terence Devlin's, advice:
You can move your iPhoto Library to an external disk pr new Mac:
1. Quit iPhoto
2. Copy the iPhoto Library Folder as an entity from your Pictures Folder to the External Disk.
3. Hold down the option (or alt) key while launching iPhoto. From the resulting menu select 'Choose Library' and navigate to the new location. From that point on this will be the default location of your library.
4. Test the library and when you're sure all is well, trash the one on your internal HD to free up space.