They're cheap, easy, go right into your itunes, and don't have funny rules attached about how many computers you can own.
My favorite thing to do right now is go to MP3 songs, and then pick a genre like...Classical, and then sort by price. Look at all of the free music!
I got a fun sampler of new Latin Music from 2009(some good, some bad), and "I Love the 80's. Volume 1 (1880s)" conducted by Marin Alsop (our somehow sometime somewhere relative). And then I made myself quit for awhile.
And Happy Kansas Day!