In this guitar lesson Damien Brown teaches you different tunings.  For your reference, courtesy of Wikipedia, here are a list of popular alternative tunings:

• D♯/E♭ tuning - D♯-G♯-C♯-F♯-A♯-D♯ / E♭-A♭-D♭-G♭-B♭-E♭
  Half a step down from standard tuning. Used by bands such as Metallica (in the 1990s), Motörhead, Cannibal Corpse (up until The Bleeding), Nirvana, Failure, Weezer, Green Day, Kiss, Guns N’ Roses, Van Halen, Brand New, Jimi Hendrix, Stevie Ray Vaughan, Yngwie Malmsteen, Alice in Chains, Slayer, The Smashing Pumpkins, Relient K, Tracy Riddle with The Polyrhythms, Suede and Beach House.
• D tuning - D-G-C-F-A-D
  One full step down from standard tuning. Used by bands such as Drive-By Truckers, Children Of Bodom, Symphony X, Death, Decrepit Birth, Dream Theater, All That Remains, Exodus, Shadows Fall, Mastodon and Kreator. Used in a vast majority of songs by musician Elliott Smith. Also used in Nirvana‘s songs Come As You Are and Lithium, by Metallica in their song Sad but True, and by John Fogerty.
• C♯/D♭ tuning - C♯-F♯-B-E-G♯-C♯ / D♭-G♭-B-E-A♭-D♭
  One and a half steps down. Famously used by Black Sabbath‘s Tony Iommi in the 1970s, as well as Carrie Brownstein, Dimebag Darrell of Pantera, Corin Tucker of Sleater-Kinney, Between the Buried and Me, All That Remains, Billy Howerdel of A Perfect Circle, and Wes Borland of Limp Bizkit. AC/DC also used this tuning in the 1970s. Also used by Kyuss on song “Isolation”.
• C tuning - C-F-B♭-E♭-G-C / C-F-A♯-D♯-G-C
  Two full steps down from normal tuning. Used by bands such as Queens of the Stone Age, Kyuss, In Flames, The Black Dahlia Murder, Dir en Grey, Dethklok, Cold, Dream Theater, Arch Enemy, The Smashing Pumpkins and the John Butler Trio.
• B tuning - B-E-A-D-G♭-B / B-E-A-D-F♯-B
  Two and a half steps down from standard tuning. Used in early Swedish death metal by bands such as Entombed, Dismember and At The Gates as well as other bands such as Type O Negative, Five Finger Death Punch and Amon Amarth.
• “Karnivool” tuning - B-F♯-B-G-B-E
  Hybrid tuning between B-tuning and E-standard. Used by the band Karnivool for their Themata album, and some of their Sound Awake Tracks.
• A♯/B♭ tuning - A♯-D♯-G♯-C♯-F-A♯ / B♭-E♭-A♭-D♭-F-B♭
  Three full steps from standard tuning. Used by Dream Theater, Adema, Cannibal Corpse and A Question Of Etiquette.
• A tuning - A-D-G-C-E-A
  Three and a half steps down from standard tuning. Used by Taproot, Dystopia, Meshuggah and Suicide Silence. Also used by Slipknot on their song Iowa.
• G♯/A♭ tuning - G♯-C♯-F♯-B-D♯-G♯ / A♭-D♭-G♭-B-E♭-A♭
  Four full steps down from standard tuning. Utilized by the band Staind as well as other variations of this tuning, it is also used by Cannibal Corpse in some songs. The Guitarist Mike Mushok uses a baritone Guitar that is specifically designed for lower tunings.
• G tuning - G-C-F-A♯-D-G / G-C-F-B♭-D-G
  Four and a half steps down from standard tuning.
• F♯/G♭ tuning - F♯-B-E-A-C♯-F♯ / G♭-B-E-A-D♭-G♭
  Five full steps from standard tuning.
• F tuning - F-A♯-D♯-G♯-C-F / F-B♭-E♭-A♭-C-F
  Five and one half steps down from standard tuning.
• Octave Tuning - E-A-D-G-B-E
  Six full steps (one octave) down from standard tuning. The Low E has the same fundamental frequency as a bass guitar, essentially the same standard tuning as a bass guitar but with a high B and E added to mimic a regular guitar. This tuning is used on the Fender Bass VI and similar instruments. Notably used by Robert Smith of The Cure and Jack Bruce of Cream.