Top Ten Pairs of Singers with Similar Voices

The lead singer of The Cranberries has a really similar singing style to Shakira, and sometimes you can't tell much of a difference except for the genre.
Examples:
"Zombie" by The Cranberries
"Underneath Your Clothes" by Shakira - Martin_Canine

Both have very powerful singing voice that often sounds like there is much pressure on the throat (I'm sure there's a professional term for that)

Examples:
"Paid My Dues" by Anastacia
"We Don't Need Another Hero" by Tina Turner - Martin_Canine

One sings English and the other one sings Italian, but both have a very nasal voice that sounds pretty similar.

"In the Air Tonight" by Phil Collins
"I Belong To You" by Eros Ramazotti - Martin_Canine

The two lead vocalists (singers and rappers) of DatAdam have extremely similar voices.

Example:
On the song "Hydra 3D" by DatAdam, verse 1 is by Taddl and verse 2 by Ardy, but I couldn't tell who is who if I wouldn't know. - Martin_Canine

Also similar genre and both great lyricists.

Example:
"Crucify Your Mind" by Rodriguez
"Times They Are A-Changing" by Bob Dylan - Martin_Canine

German jazz singer Annette Louisan and leas singer of German alternative pop band Wir sind Helden Judith Holofernes both have very high pitched and soft vocals.

Example:
"Torsten Schmidt" by Annett Louisan
"Gekommen um zu bleiben" by Wir sind Helden - Martin_Canine

Maybe due to them singing the same genre, but former Nightwish singer Anette Olzon and Beyond the Black singer Jennifer Haben sound pretty similar to me. Both have unusually pop-rockish vocals for symphonic metal.

Examples:
"Amaranth" by Nightwish
"Written in Blood" by Beyond the Black - Martin_Canine

Before Bill Kaulitz from Tokio Hotel had his puberty voice change, he sounded a lot like female German rock singer LaFee.

Example:
"Durch den Monsun" by Tokio Hotel
"Prinzesschen" by LaFee - Martin_Canine

Maybe it is due to me not actively listening to RnB, but most contrmporary RnB singers sound extremely similar to me, especially Taio Cruz and Chris Brown.

Example:
"Dynamite" by Taio Cruz
"Right by My Side" by Nicki Minaj & Chris Brown - Martin_Canine

Both are metal singers with great tenor voices. Also, Tobias Sammet singing style was influenced very much by Bruce Dickinson. Tobias Sammet voice always reminds me of Bruce Dickinson.
I even made a list - Top 10 Edguy Songs that Could Be on Iron Maiden Albums - Metal_Treasure

Danzig - Mother, Am I Demon, How The Gods Kill. - Metal_Treasure

Rob Halford of Judas Priest and Ralf Scheepers of Primal Fear - both are metal singers. Halford is Ralf Scheepers' biggest influence and Ralf Scheepers sounds pretty much like his vocal idol:
Scheepers - Before The Dawn (solo album, 2011)
Primal Fear - Strike, Metal Gods (Judas Priest cover). - Metal_Treasure

Check out these cover versions of Coverdale songs and be convinced:
Jorn - Stormbringer, Burn (Deep Purple covers)
Jorn - Fool for your loving (Whitesnake cover) - Metal_Treasure

Stu Block replaced Matt Barlow in Iced Earth. I am pretty sure that Stu Block got the job because his voice sounds similar to Matt's voice. - Metal_Treasure

Brian Johnson of ACDC and Mark Tornillo of Accept. Since everybody knows Brian Johnson and his voice, I am gonna list only Mark Tornillo songs:
Accept - Pandemic, Shades Of Death,Teutonic Terror. - Metal_Treasure