I buy CDs.
I'd rather have it just in case something happens to my iPod or iTunes account, I can always put the songs back on to it.
I also buy CDs so I can listen to songs I like, instead of listening to streaming music which constantly plays the same songs over and over, and if you want to hear the song again, you can't hit a replay button. On CDs however, you can replay the song you've just listened to and if you're tired of one CD, you can exchange it for another and listen to that one.
I also buy CDs due to them (most of the time) having something extra such as a poster, autographs, maybe even some sort of clothing inside (at least some sort of extra or "prize").
I enjoy getting extra things, but I buy CDs for a more important reason, it's to finacially support the bands and singers I listen to. Most people don't know this, but a wide majority of bands would and have made more profit off of CDS rather than iTunes. CDs tend to be more expensive than songs and albums on iTunes, but that's how the bands/singers/musicians get their money to support themselves. A song off iTunes usually cost $0.99 to a little over a dollar, and albums may cost some where around $9.99 and a little over. CDs cost around $13 and up. Because of this most people won't buy them, but if they add that 'extra' (poster, autograph(s), clothing, etc.) it draws more attention to it for people to buy it.
So if you really want to support your favourite bands, singers, musicians, etc., buy CDs.
(Buying merch. from them helps too.)