back in July, there is an excellent series of "99 most essential" works from various classical composers offered as MP3 collections from X5 Music Group. The regular prices are in the $6 to $8 range, which is a good deal for many hours of quality classical music. But Amazon sometimes offers introductory specials on new collections for around $2, which is a crazy good deal (about 2 cents per musical piece).
Recently two new composer collections were released, Dvorák ($2.49) and Grieg ($1.99). I had only heard a few of their best known works before, so I was happy to expand my knowledge and my music collection for just a couple of bucks. The MP3 sound quality is good and most of the multi-movement works are included in full (all movements in order), though there are also some excerpts.