And don’t forget The Fall.
I’m not sure if this fits, because their musical styles are different, but I get Creedence Clearwater Revival (CCR) confused with Crosby, Stills and Nash (CSN). If I hear a song by one of the two, I have to stop and think before I know which group it is. Three names, first name begins with CR, three initials, early 70’s (before I was aware of music) … that’s enough to confuse me.
Or more recently, the British band Bush had to call themselves “Bush X” in Canada for a couple of years, because someone else had dibs on Bush at the time.
That’s exactly what I was getting at. Not to mention Three Days Grace sound nothing like 3 Doors Down or Third Eye Blind (who, I’ll grant, do sound a lot alike).
There’s Beck and Jeff Beck
I have a song from a rap contest by a guy who calls himself “Skeem”. I’d love to hear more of his work. Unfortunately there’s about eight hundred thousand crappy amateur rappers who also call themselves “Skeem”.
I used to confuse ColdPlay and Snow Patrol both for their names and their sound.
Also, Squeeze were known as “UK Squeeze” when their first album came out.
I used to resist the “English” in The Beat - but it’s easier to sort my iTunes with “English Beat.” Otherwise I get “Lucy in the Sky With Diamonds” playing alongside “Stand Down Margaret.” 
Depends on what kind of music you’re into. Assuming you stay in the same genre, in the whole grand scheme of things almost any 10 year period in music history is going to produce music that is theoretically very very similar.
Pandera (Africanesque melodic trancy pop/reggae) and Pantera (angry thrash metal).
The former which I discovered via Pump It Up, the latter via Guitar Hero. Damn, I love this modern age.
As for name addendums, I nominate, of course, Puffy Amiyumi. Simply “Puffy” in their homeland, a certain well-known rapper necessitated a slight modification once they became pouplar in America.
On a related note, can anyone tell me why Smile had to add the “.DK”?
I get confused by Harvey Danger and Marcy Playground.
Too bad you didn’t find them through Pandora!
Yes! Also, though obviously not for their sound, my brain switches up Puddle of Mudd and Jars of Clay (inanimate objects maybe?)
and to a lesser degree, Mustard Plug vs Skankin Pickle (ska bands and condiments?)
Army of Me
Army of Lovers
Army of Robots
Army of Freshmen
Army of One…
I’m only vaguely familiar with any of them, so I can never tell them apart. I don’t understand the proliferation of military names: besides the above there’s also Army Navy, New Model Army, Tiger Army…Tigers are pretty popular too, actually: Tiger Baby, Tiger Trap, Kissing Tigers, Faster Tiger, The Republic Tigers, The Papertiger Sound…
Is there more than one band named Atmosphere, or one just really eclectic band? I’ve heard 3 songs by “Atmosphere,” two hip-hop, one electronica.
Is Dusty Buffalo Springfield still around? Is she stll married to that Rick guy?
Don’t forget Three Colors Red.
In my ignorant youth I would have sworn that the latter morphed into the former (as the Cult did in the 80’s, dropping “Southern” and then “Death” from their name in succession).
The latter group actually annoyed me, as I was a fairly big fan of the former, and then these upstart Pipe guys came along during a hiatus in the Verve’s output and in my mind kind of stole their thunder, if not part of their name, a bit. Urban Hymns kind of switched that back around. Checking Wikipedia I now see that the latter was founded a mere year after the former-still bugs me tho. Don’t grok why they didn’t change the name once the British group got lots of visibility with their debut c. 1994-wouldn’t have been the first fledgling band to do so (c.f. the Beatles, or Joy Division).
Can’t forget about Kate…
Even now I have to think about which one is who there for a second or two. After all Buffalos often leave the plains all dusty with their passage. The band should have hired the girl to sing for them during a one-off concert or something (they were both folk rock after all).
Lush & Luna is my original contribution. Even now without consulting an online reference I don’t know which one has the cute Asian blonde lead singer (the band I favored back in their collective heyday).
Oh, and Nelly NoLastName, and Nelly Furtado. Underwent a similar back and forth ebb and flow popularity duel as the Ververs did.
First one that came to mind is Rocket from the Tombs and Rocket from the Crypt.
There’s always Tilt, Tilt, and Tilt.
I used to get Schoolyard Heroes mixed up with another band, but I can’t remember who. It wasn’t Marcy Playground, but someone with a word similar/opposite to either schoolyard or heroes- something like playground or bully.
The Bangles and The Buggles.
Is it Gym Class Heroes, perchance?