Last week we were supposed to get the major label release of Odd Future cohort Frank Ocean's debut project, nostalgia, ULTRA, previously a mixtape. Unfortunately, the suits at Def Jam have apparently stricken it from the upcoming-release schedule, with Ocean reacting by releasing the gratis download “Thinking About You,” a low-key, muted affair.

But beyond his solo ambitions, Ocean is part of a select club of singers who are firmly aligned with rap troops. These folks aren't rappers who also dabble in singing — like, say, Drake or Lauryn Hill — but crooners who at one point started rolling deep with rap groups. Here, then, is a salute to the five best rap hook troubadours.

5. Frank Ocean

While Tyler and company were busy developing their rhyme styless, the kid born Christopher Breaux decided to stick with his singing talent. It's a move that seems to be paying dividends, with collaborations and song-writing stints for John Legend and Beyonce in the pipeline, not to mention two coveted guest spots on Kanye West and Jay-Z's soon-dropping Watch The Throne. With an ability to sing in sober and carefully-reserved nuances, the smart money is on Ocean ultimately becoming the Golf Wanger with the longest and most fruitful career.

4. Sleepy Brown

Long before Andre 3000 discovered that he quite enjoyed singing in the shower, the Dungeon Family called on Organized Noize producer Sleep Brown to add vocals to their down south rap tunes. Brown was a constant presence during the crew's formative years, providing backing vocals to Goodie Mob's “Soul Food” and Outkast's “Elevators (Me & You),” and he continued to spread love the southern way with assists for Bubba Sparxxx's “Back In The Mud” and Ludacris's “Saturday (Oooh! Ooooh!)” (although, in fairness, Brown is wholesale upstaged by a rooster and a chicken in the video for the latter). Perhaps most memorably, Brown's slick and sophisticated vocals propel Big's slinky “The Way You Move.”

3. TJ Swan

The pioneer of rap warblers, TJ Swan held down chorus duties for Marley Marl's golden era rap giants the Juice Crew. Swan is best remembered for his vocals on hip-hop clown prince Biz Markie's late-'80s anthem “Make The Music With Your Mouth, Biz,” and for providing the chorus chatter to MC Shan's sorrowful “Left Me Lonely.” His partnership with Biz also led to a tribute to the now defunct Brooklyn shopping emporium Albee Square Mall, which included the triumphant closing refrain of, “Go shopping, go shopping, let's all go shopping!” (Outside of the Juice Crew's kingdom, Swan also added the hook to Kid Capri's smoothed-out “This Is What You Came Here For.”) Rap geek interest in a long-lost and unreleased TJ Swan album, possibly titled Have No Fear, Swan Is Here, was tempered by the underwhelming “Mellow Love,” but Swan's status as an originator of the discipline remains irrefutable.

2. Pharrell

Pharrell Williams's reputation as a hit-making producer is well known, but his role as a hook-singer-for-hire is unheralded. He's the guy bringing the falsetto funk to Jay-Z's “I Just Wanna Love You (Give It 2 Me),” the elated trill to Busta's “Pass The Courvoisier,” and the one who helped sling Luda's “Money Maker” to the top spot. Outside of the glitzy platinum hit circuit though, it's Pharrell's work with his de facto in-house rap group The Clipse that asserts his hip-hook credentials. You could make an entire mixtape of his ad libs and chorus crooning for the brothers Thornton, and it would be a fine example of rap ignorance par excellence, sparkling with declarations like, “Motherfucker hit you then better hit them back/So when I hit the n*gga he quit playing!” Pharrell's hollers alone on mixtape cut “Studyin' Y'all” sound like a man on the verge of having an orgasm after perusing through a glossy gun catalog. If you want someone to sing enthusiastically about drugs and high-powered weaponry, Skateboard P is that man.

If you can't guess number one, what are you doing on this blog?

1. Nate Dogg

“Well you all know Nate Dogg, who sings on my records,” rapped Snoop on his cover of Biz Markie's “Vapors.” With that, tha Doggfather gave Nate Dogg the same place within the Dogg Pound that TJ Swan had in the Juice Crew. Blessed with a baritone bark of a singing voice, Nate Dogg came to fame during the g-funk era: Pulling off the opening to Snoop's “Ain't No Fun (If The Homies Can't Have None)” without breaking into a laugh still stands as a feat of high studio professionalism. But beyond adding cavernously-sung hooks for his g-funk cronies, Nate's vocals proved an adept mesh with many a rapper's lyrics; he was called on by Eminem for “Bitch Please II”, gave New York under-sellers Mos Def and Pharoahe Monch a decent sized hit with “Oh No,” and then starred on 50 Cent's chart-topping, fat kid-baiting “21 Questions.” Nate Dogg passed away earlier this year, but his legacy as every rapper's ultimate hook singer will forever live melodious.