where can i get high quality downloads?

Hi,

The last hifi i bought was an arcam alpha 3 amp and marantz cd52 and KEF speakers when at school; as you can see i have been out of the hifi world for quite a while. A new flat and time to improve on the ipod dock and the qute has caught my eye. Ive longed for naim kit since i was a kid and the size and features also impress the other half, however my ipod is full of poor quality downloads so was wondering where, apart from itunes, can i get top quality music and what would be the minimum requirement to sound good through a qute?

I want to start re downloading my collection before i get the qute and get frustrated with poor downloads.

Thanks in advance.