Apparently the #2 music store on the internet (behind itunes) which is some accomplishment considering the general lack of mainstream music. Despite this there is a wide variety of music available, from Woody Guthrie to Sufjan Stevens and Cat Power. There is a definite weighting towards indie-type bands and an excellent selection of jazz - with many other genres. Mp3 format only (high bitrate VBR). Payment is on a subscription basis and prices are very reasonable.
Another shop with a good selection of indie bands. High bitrate VBR mp3s and a select few Flacs are available (their FAQ says they're considering expanding their FLAC collection which would be fantastic). Available worldwide. Pay on a per-album or per-track basis. Looks more expensive than emusic but would be a good choice for getting just one album…