Agree with everyone else, Adobe CS4 is the way to go, no doubt.
Dont forget though, if your son is doing a course, or is still at school or college then you may be able to get it at a
student rate (a huge saving), just something to look into.
Check this page on their site;
Buy Adobe Creative Suite Design software online at lowest UK price :: eCostSoftware.com - UK Software Supplier
it lists the full CS4 package that will have everything he'll need - InDesign & Photoshop being the main ones, along with Dreamweaver (web design) and Illustrator for working on vector graphics etc.
The Adobe CS4 Design Premium should have everything to get him started -
Adobe's Site