There are many reasons a band might release a Greatest Hits or live album. More often than not it comes down to contract fulfillment: maybe they broke up before recording all of the albums they'd signed on to do. Maybe they switched labels before the end of their agreed term and had to make up the difference.

Maybe it's been a while since their last studio album and they're heading out on the road on a major tour, and it always helps to have something in stores to both promote and be promoted by the tour. Maybe they just simply have a whole bunch of hits, and it'd be nice to have them all together in one place.

Whatever the reason, one of the greatest things about a greatest hits album, for me, has always been the opportunity to hear a rare or new track. Here are a few of my favorites, but feel free to leave yours in the comments section!

Led Zeppelin – “Baby Come On Home” from Boxed Set 2

Led Zeppelin

“Baby Come On Home” is the jewel in the crown of the un-inspiringly named Led Zeppelin Boxed Set 2, the 1993 companion set to the 1990 Led Zeppelin box set. This two-disc set includes the rest of Led Zeppelin's discography not already included on the earlier four-disc set. And “Baby Come On Home” was an unused track originally recorded during the sessions for the band's debut album. The master tape (labelled Yardbirds. October 10, 1968) went missing, allegedly showing up in a refuse bin outside Olympic Studios in 1991. Based on two songs by Bert Berns but with rewritten lyrics, the track is an R&B ballad featuring Jimmy Page playing guitar through a Leslie while John Paul Jones contributes Hammond organ and piano. The song hit #4 on the Billboard Mainstream Rock Tracks Chart.

Van Halen – “Can't Get This Stuff No More” from Best Of Volume I

Van Halen

Between their two best-ofs, Van Halen have recorded five new songs: two with David Lee Roth (“Can't Get This Stuff No More” and “Me Wise Magic” for Best Of Volume I), and three with Sammy Hagar.

Of those five, “Can't Get This Stuff No More” is the real standout. It doesn't exactly pick up where Van Halen left off at 1984, but it does sound like exactly what it is: something that those same four musicians might have recorded 12 years later. David Lee Roth's lyrics are typically 'Dave' - which is to say, not particularly sensical but no less entertaining for it - while Eddie seems absolutely inspired on guitar.

It would be another 16 years before Van Halen and Diamond Dave would release new music together again - the critically-acclaimed A Different Kind Of Truth - but “Can't Get This Stuff No More” and “Me Wise Magic” seem to have been lost in the shuffle. Perhaps one day they'll be brought out for live performance.

Joe Satriani – “Time Machine” from Time Machine

Time Machine is a weird entry in Joe Satriani's discography. It's a two-disc set which combines one CD of outtakes, jams, rarities and tracks from Joe's original self-released, self-titled EP, and another CD featuring live material culled from 1988 and 1992. And it kicks off with three new recordings: “Time Machine” (an epic, lumbering, progressive slab of drop-D semi-psychedelia); “The Mighty Turtle Head,” a bluesy finger workout; and “All Alone,” an arrangement of “I'm Left Alone,” a song written by Billie Holiday and pianist/composer Mal Waldron. All of the new recordings are worthy of inclusion but the title track has particularly endured in the hearts of fans, even inspiring the cover of an issue of IDW's comic book Eternal Descent.

Black Sabbath – “Psycho Man” from Reunion

Black Sabbath

Black Sabbath's 13 is definitely one of the albums of the year, but amid all the excitement for new Black Sabbath material it's easy to forget that we've already had a few 'new' Black Sabbath tracks for over a decade. Released in 1998, the live album Reunion featured two new tracks, “Psycho Man” and “Selling My Soul.” Of the two, only “Psycho Man” features original drummer Bill Ward: a drum machine is featured on “Selling My Soul.”

“Psycho Man” is a good song and it's definitely worth revisiting from time to time, but it's not as developed and all-out massive as the material on 13. And for that matter, not as realized as the three songs Sabbath later recorded with Ronnie James Dio for the Black Sabbath: The Dio Years compilation in 2007 (“The Devil Cried,” “Shadow of the Wind” and “Ear in the Wall”).

The Beatles – “Free As A Bird” from Anthology 1

The Beatles

The death of John Lennon in 1980 meant we'd never see a Beatles reunion, but in 1994 the remaining members of the band gathered to record together on a few home demos Lennon had recorded in the 70s.

Of the two – “Free As A Bird” and “Real Love” - the former was the bigger chart success. Co-produced by Jeff Lynne of Electric Light Orchestra and with a beautiful video directed by Joe Pytka, the song met with mixed critical reception at the time, but on reflection it has a certain haunting beauty. The video for “Real Love” is also beautiful in its own way, as it features footage of Paul McCartney, Ringo Starr and George Harrison recording together during those 1994 sessions.