Well, after the first paired couplet in which the singer invites his ladyfriend to inform her parents that he’s relocating her in Bill Clinton’s home state, Mr. Ray Charles’ classic “What’d I say?” features a wonderful economy of lyrics.
Who can forget the compelling understated austerity of the chorus?:
The man could have sung the telephone book backwards and made it hummable.
Santana - Jingo (3: jingo, lo, ba)
Enya’s “Sail Away” features a little mumbling, but it’s mostly just the two words in the title.
There’s a huge heap of electronic music which features a single word lyric or a repeated short phrase. Probably not what you’re looking for though.
S.O.D.'s “The Ballad of Jimi Hendrix” (Two: “He’s dead”)
I’d nominate the WKRP ending theme, except that I don’t think there’s a single word in that whole mess.
Elton John’s “Song for Guy”:
Life
Isn’t everything
(repeated about a zillion times)
The Robert Fripp version of “Exposure” from the album of the same name. The lyrics are mostly someone saying the word very slowly repeatedly as someone else spells the word repeatedly.
The Peter Gabriel version has some lines about “Space is what I need, It’s what I feel” mixed in with the repetition of “exposure” but no one spelling on that one.
The Everclear instrumental song “El Distorto De Melodica” includes an evil sounding laugh and a processed scream but no real words.
The song is properly titled “Orinoco Flow (Sail Away)” and is anything but a “little mumbling” and the two words. Sorry.
dj shadow’s “why hiphop sucks in '96”: 3 words.
“it’s the money.”
Daft Punk’s Around the World repeats the title for about seven minutes. That’s only three words.
And there was a hardcore techno track out a few years ago by Hocus Pocus called Here’s Johnny. It’s only lyrics were the two word Jack Nicholson sample from The Shining.
I think Adult.'s Nausea only has the word naws-ya! repeated over and over, but I couldn’t be sure.
Well, even though he was in elementary school at the time - maybe we can point a finger of blame at Bill Gates for this is it 13 or 14 words dilemma.
In his Word program, noone (as opposed to no one) comes up as acceptable in the grammar check and on the thesaurus as a synonym for ‘nobody’ and ‘not a soul’.
I was always taught there wasn’t any such word as noone and Webster’s online confirms that…but who am I to argue with a billionaire?
Thank you JohnBckWLD. I put “noone” as one word, too.
As for IWY(SSH), I was going by memory and using my fingers to count at the same time–obviously, not a fruitful combination. 
Gary Moore’s The Loner has the lyrics of Loner. There might be one or two other words in there like The, but that’s about it.
“Sex and Violence” by the Exploited repeats the title over… and over… and over. That’s the whole damn song.
There are all the Dwarvish drinking songs from the Discworld :
“Gold, gold, gold, gold,
Gold, gold, gold, gold,
Gold, gold, gold, gold,
Gold, gold, gold, gold…”
I may have skipped a post, but I thought someone would have remembered "Rock 'n Roll, Part I by Gary Glitter
Church Key - The Revels
Let’s Go Trippin’ - Dick Dale
Ma-na Ma-na (wan’t this song used in a Lipton tea commercial?)
O.K. I’m dialed-in…
“One Step Beyond” - Madness
Nit Pick: I thought the lyrics were “You’re dead”.
They also have the song “Diamonds and Rust”. I bet you can guess the lyrics. Hint: 3 words in song’s title.
These “songs” are only a few seconds long but I guess they are considered songs.
Motley Crue’s “God Bless the Children of the Beast” has these words sung at the end of a short instrumental piece by the same title on Shout at the Devil.