Unfortunately the ipod is locked into itunes for drm music, completely. Check for playforsure compat. with your brother's player though, he may have some hope yet!

Emusic downloads are drm free, and thus playable on your ipod, but their selection is pretty obscure for the most part. Lots of smaller/emerging artists/grps.
I think the BEST service I have come across is Virgin Digital, if for the simple fact that you get music insurance - ie: if you lose your entire collection in a hard drive crash etc, you can re-download it again at no cost at all to you. It keeps a track of everything you've downloaded to own forever.
However, this is playforsure drm, and again, won't work on your ipod.
Depending on how much you love your ipod, I'd suggest you exchange it or sell it and get either a playforsure compatible mp3 player, such as a creative labs zen vision or something OR get the zune - MS has it's own subscription download service with about the same number of tracks as most of the other services and it'slike 14 or 15 a month. If you really want to stick with the ipod, then you'll have to go with a service that doesn't drm tag their music, like emusic and, well, allofmp3 which is unfortunately quite illegal according to just about everybody but them.
Here's the site that gives you most if not all playsforsure devices available. You should be careful when buying new devices however, as we don't quite know what the future holds for this drm technology, as MS has both dropped the tech, as well as closed its own service that used it.
http://www.playsforsure.com/Good Luck.