This won't be a very tough sell to Indigo Girls [ tickets ] fans. For this group of ardent followers, which ranks just below Trekkies in terms of unbridled passion, anything that carries the Indigo Girls' name is a must buy.

It's a much harder sell for the casual fan, the one that might only know "Closer to Fine" and a few other big numbers. The album hardly ranks among such Indigo Girls gems as 1989's self-titled release, 1992's "Rites of Passage" or 1995's live "1200 Curfews."

The 18-track collection, which features demos, previously unreleased material, soundtrack work and contributions to tribute and benefit albums, does have some nice moments. Some of the best offerings include a solid take on the classic punk track "Clampdown," from 1999's "Burning London--The Clash Tribute," and a worthy reinterpretation of Vic Chestnut's "Free of Hope," originally recorded for 1996's "Sweet Relief II: Gravity of the Situation." "Rarities" also features a few strong collaborations, the best of which features R.E.M.'s sensational Michael Stipe joining forces with Amy Ray and Emily Saliers on "I'll Give You My Skin."

There are also quite a few low points. The duo's take on "Uncle John's Band," from 1991's "Deadicated: A Tribute to the Grateful Dead," feels quite shallow. Audioslave's Tom Morello uses a very heavy hand to remix "Shed Your Skin," and the result comes across like a poor imitation of the great Patti Smith. With any luck, those numbers--as well as a few others--will remain true "Rarities."