The Indigo Girls [ tickets ] have added another half-dozen dates to their 2008 outing, which is currently set to comb the eastern US.

The folk-rock duo will play a holiday concert this month in Tucson, AZ, before launching the tour Jan. 24 in Athens, GA. Since last check, shows have been added in Chicago; Columbus, OH; Richmond, VA; Asheville, NC; Charleston, SC; and Knoxville, TN. Additional dates are expected, according to the Girls' website. Confirmed gigs are listed below.

Genre-bending singer/songwriter Brandi Carlile is scheduled to open dates through Jan. 29 and folk-rocker Michelle Malone will take over from there.

The Indigo Girls toured North America all spring and summer and recently returned home from Australia, where they hadn't played in nine years.

The Girls are supporting last year's "Despite Our Differences," their 10th studio album and first for Hollywood Records. The set, produced by Mitchell Froom (Paul McCartney, Sheryl Crow), marks Amy Ray and Emily Saliers' 20th year of performing together. In that time, the Grammy-winning duo has sold more than 12 million albums, according to a press release.

Ray is also staying busy with her side project, Amy Ray and the Volunteers, which is getting ready to offer its latest project, "Live from Knoxville," as a digital download. The limited-edition set, released on Ray's own Daemon Records label, will be available for digital download beginning Dec. 19 at the eMusic website and at other music-download sites in February.