On the Ambient tip: "Thursday Afternoon" by Brian Eno is strange and wonderful - and is probably one of the longest tracks ever at 61 minutes - DJs who like a long dinner break take note.
On the Blues Tip: "Season of the Witch" by Al Kooper, Mike Bloomfield and Steven Stills.
On the Dance tip: Pretty much anything with 180-220 bpm'll do, really
However... "The Hangar" by Eat Static is extremely frenetic, "Blue Room" by the Orb and Aphex Twin's stuff needs mentioning.
On the Goth tip: "Bela Lugosi's Dead" by Bauhaus (I think the live 12" version weighs in at over 10mins).
On the Hip hop tip: "Rapper's Delight" by the Sugarhill Gang.
On the Jazz tip: "B*tches Brew" by Miles Davis is grand as is his "In A Silent Way". "Nighthawk Postcards (From Easy Street)" by Tom Waits is a wild and wooly story with a great jazz backing.
On the Psychedelic t(r)ip: "Voyage 34" or "Moonloop" by the Porcupine Tree. "Jurrasic Shift" by the Ozric Tentacles also needs a mention
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On the Rock tip: 2 tracks - (but they do segue and the first is over 10mins) - "1983... (A merman I should turn to be)" and "Moon, Turn The Tides... gently gently away" by the good old Himi Jendrix Interference.