Gregg Rolie was actually Journey’s original lead singer. The band brought in Steve Perry aftertheir first several albums, and the original intent was apparently that Perry would be the lead singer, but that Rolie would continue to handle some of the singing, as well. That only lasted for a couple of albums, before Rolie left.
My Wife is really well-known.
Ringo Starr sang Yellow Submarine, right?
NM
The track was sped up.
R.E.O. Speedwagon’s best song (imho) was written and sung by the bass player, Bruce Hall.
Yeah, I hear “My Wife” on classic rock radio relatively often, but “Boris” doesn’t come up very often.
Entwistle wasn’t the only “singer who’s not the lead singer” in The Who, either. Each of the original members of the band sang lead vocals at least a couple of times, but after usual lead singer Roger Daltrey it was Pete Townshend who sang most often. I think the only song with Townshend on lead vocals that was a “hit” in the sense of being a single that charted was “Eminence Front”, but he sang a couple of other fairly well-known Who songs such as “Acid Queen” on Tommy.
And what is that song? Just curious.
Mike Mills sang lead on two notable R.E.M. songs: “Superman” and “Texarkana.”
Andy Partridge is generally known as the lead singer of XTC but bassist Colin Moulding sang lead on a number of big XTC hits: “Making Plans for Nigel,” “Generals and Majors,” “Life Begins at the Hop,” and “Ball and Chain,” to name a few.
The Clash’s “Guns of Brixton” was sung by Paul Simonon.
He also sang lead on “Near Wild Heaven”. Never heard that song before. 
How odd. I’ve seen that video for ‘Making Plans for Nigel’ more than once and never noticed it wasn’t Andy.
“Tuesday Morning” by The Pogues, one of their most successful singles, was sung by Spider Stacy, as Shane Macgowan had left the band by that point. Spider was arguably the lead singer of the band at that point, although several members sang on that album, but he’s certainly not the singer most people think of when they think of The Pogues.
Ann Wilson normally sings the lead for Heart, but their biggest hit was “These Dreams”, sung by Nancy Wilson.
The Eagles single *Take It to the Limit * was the only A-side on which Randy Meisner sang lead.
Mickey Dolenz of The Monkees sang * Last Train to Clarksville*, (I’m Not Your) Steppin’ Stone and * A Little Bit Me, a Little Bit You*.
George Harrison did lead vocals on While My Guitar Gently Weeps, Something, and Here Comes the Sun for whichever band he was in. I recall the exact “who’s that” experience first time around.
Derek Holt penned and sang “I Love You”, which was a tribute to his wife and was one of the Climax Blues Band’s biggest hits. The band hated this lovey dovey song and rejected it and refused to sing on it. So Holt decided to record it himself with help of the drummer and famous Nicky Hopkins on piano. It becomes big hit but the other singers refused to perform it. It fact, it has never ever been sung live They also vetoed it from other compilation albums and for a while the song went missing when they stopped printing the original album. This is probably the main was the song wasn’t a bigger hit and the band even more popular.:o
Carl Wilson did the lead vocals for the Beach Boys’ “God Only Knows.” Not sure if it was technically a hit, but certainly was one of the three most popular tunes on their (by far) most critically-acclaimed album. (Lead vocals in the band were generally by Brian Wilson or Mike Love, or sometimes Al Jardine – Carl and Dennis mostly contributed harmonies.)
The Allman Brothers Band’s first and only top ten single, topping out at #2 on the Billboard Hot 100 chart was Ramblin’ Man, sung by Dickey Betts.
I think Keith Richards does a fine job on Slipping Away.
I consider The Band’s Levon Helm to be the lead vocalist, but Richard Manuel does I Shall Be Released better than anyone.
This may not be exactly what you’re looking for, but: My earliest awareness of The Alan Parsons Project was from hearing “Eye in the Sky,” “Time,” and “Don’t Answer Me,” so I associated Eric Woolfson’s voice with the band, and only discovered after I started buying their albums that, far from being the lead singer, he only sang lead on a relatively few songs.
We had a similar thread a while back: Best songs not sung by the lead singer.
Also on “Good Vibrations,” and more after Brian Wilson’s involvement in the band diminished post-Pet Sounds.
Night Ranger’s drummer sang lead on Sister Christian, which if it wasn’t their biggest hit, it was damn near.