Apple continues to confuse us (or at least me). There was no Discovery Download yesterday, and today there is one, but you can't get to it. The song is "Something More" by Sugarland, from the album "Twice the Speed of Life", but clicking the link produces the message shown below.
It could be that this song will become available before next Tuesday, or be next week's Discovery Download instead of this week's, or be one of two Discovery Downloads next week. If Apple can't put the comma in the right position in a date ("October, 26 2004") then it's no surprise they get the Discovery Downloads mixed up now and then!
Update, Wednesday evening: The free tune is now available, but clicking on the album link still produces the message "The item you've requested is not currently available in the US store."