I second Elizabeth Mitchell. My kids are big fans of the second Dave Matthews CD -- Under the Table and Dreaming.
Dog Train -- it's actually a Sandra Boynton book that comes with a CD. She wrote the songs and they are sung by varius artists. My kids love it and the music is completely tolerable.
On a less tolerable side, but my kids like, the Little People CDs and Juno's Rhythm Adventures, or something like that. While the singing on the Juno CD is somewhat annoying, the second half of the CD is all instrumental and the music is good.