Massive Attack - Unfinished Sympathy (1991)

Arguably one the best songs of the 90's, Massive Attack's Unfinished Sympathy combined elements of soul, hip-hop and orchestral strings to give an unprecedented sound which put Massive Attack's name on the map. Shara Nelson's moving vocal performance on this track is enough to send shivers down anyone's spine. Great song, great record sleeve, great video, great album; seems to tick every box. Also the Oakenfold remix was as good as the original and they are both on a par for me. A truly breathtaking piece of music.
The percussion loop on the original version is sampled from the song Parade Strut by J.J. Johnson from the 1974 soundtrack of Willie Dynamite. The voice at the beginning of the song is a sample from John McLaughlin and the Mahavishnu Orchestra's Planetary Citizen.

The Paul Oakenfold mix:

Incidentally, the reason why the group were called 'Massive' at the time was because the name 'Massive Attack' was deemed by EMI as being insensitive seeing as the First Gulf War was going on.

And you thought political correctness was a new thing...

The Winstons - Amen Brother

Never heard of this track? Oh yes you have, or at least a small part of it. The drum solo at 1:27 - 1:33 was sampled; music history made in 6 seconds and spawned several entire subcultures.
But first, let's shed a little light on The Winstons themselves.
They were a 1960s soul/funk group, based in Washington, D.C., who are most notable for recording a track called Color Him Father recorded in 1969, backed with a B-side entitled Amen, Brother, with that sample in question.
It's probably the most sampled record of all time. The drum solo (performed by G.C. Coleman) that has been sampled and used in thousands of hip-hop, pop, drum and bass and jungle tracks. This beat is known as the Amen break, after the song.

Can't hear it? let's make it simpler:

The musicians must be rolling in it, yes? Er, no. Neither the Winstons, Coleman, nor the copyright owner Richard L. Spencer have ever received any royalties or clearance fees for the use of the sample, nor have they sought royalties.
If you're of a mind to, get comfy and watch this, it explains the sigificance of Six Short Seconds:

The Mohawks - The Champ (1968)

Oh man, this is a good one; funky ass organ mover if ever there was!
The Mohawks were a band formed from session musicians and fronted by the undisputed king of Library music composers, Alan Hawkshaw. The Mohawks were never actually a 'touring' band, but rather the clever idea of some guy at KPM music in the 60's who decided to release a bunch of incredibly groovy and funky library music tracks and package it under the name "The Mohawks".
The Champ is also a widely known song for having been sampled in so many other songs, notably because the actual word they're shouting in the songs opening and chorus is actually Tramp, which may or may not have anything to do with it's popularity amongst hiphop artists. One could also argue the point that the beat is so genuinely great, making it an obvious candidate for popularity.

Sample Check: too many to list (like over 100 according to my reckoning), but notable ones include Eric B Is President by Eric B & Rakim, Groove Me by Guy and Smooth Operator by Big Daddy Kane.

Incognito - I Hear Your Name (1995)

Another tune I have on regular repeat on my Zen player and one of my all time Cog vocal tracks - it's so uplifting and I used to get goosebumps when I heard it played on the radio driving to work when it first came out. I had exactly the same feeling when I heard the song played live at the last gig I saw them at in the Forum Kentish Town.
Vocalists are Joy Malcolm (who's worked with such people as Chaka Khan, George Benson, Roy Ayers, Drizabone and Jocelyn Brown, to name but a few) and Pamela Anderson (not to be confused with that Pamela Anderson), Pamela or P.Y. Anderson who's worked with D-Note. Her sisters are Jhelisa and Carleen Anderson and if you aren't aware, their Dad is Donald Byrd.

Raphael Saadiq feat. Stevie Wonder and C.J. Hilton - Never Give You Up (2008)

From his 2008 album The Way I See It, Ex-Tony! Toni! Toné! frontman Raphael Saadiq's fourth solo outing was critically well-received, made several critics' 2008 best albums lists, and garnered three Grammy nominations including Best R&B Performance By A Duo Or Group With Vocals (for this track); Best Traditional R&B Vocal Performance (for Love That Girl) and Best R&B Album for The Way I See It. C.J. Hilton, the son of a gospel vocalist, is a talented writer, producer and multi-instrumentalist.
Raphael is on his usual fine form while Hilton is channeling Marvin Gaye in his vocal delivery; at some points he sounds like a dead ringer for the man. And yes, the soloist on the harmonica is by living legend Stevie Wonder, doing as only he can. And a head nod of respect from Raphael to introduce such an icon, much like Stevie introduced Dizzy Gillespie on Do I Do.