Ok, it's on TV all the time but should you want to have the collection on DVD, then Amazon currently have the Friends series 1-10 boxset for only £39.68. It's the 15th anniversary edition so it has loads of extras too.

I've bought this one for my sister. Just need to get her a DVD player now so she can watch it in her room and Friends won't be on in the living room all the time hehe.

Friends - Season 1-10 Complete Collection @ Amazon