One of the real joys of Top 40 radio back when it first got underway, say 1955, was the real variety of music that was played and charted.  Pop, Jazz, Country, Foreign, and a few more.  I was exposed to pop music early on in my life, thanks to my Dad, so I still have a wide appreciation for all kinds of recordings.  I thought that I would list a few categories over the next weeks just to salute those that made the hits that blasted out of my transistor radio.
I'll start with the male vocalists, the guys that were at home on the nightclub stage, were considered M.O.R. (middle of the road) and were likely popular before Top 40 radio took over.  I'm going to list them, along with the number of Top 20 hits they had on from 1955.  I'll also list one of their hits.  Feel free to add on if I miss someone.
1)  Perry Como (20)  "Catch A Falling Star"
2)  Nat King Cole (15)  "Rambling Rose"
3)  Frank Sinatra (13)  "Strangers In The Night"
3)  Andy Williams (13)  "Can't Get Used To Losing You"
5)  Johnny Mathis (10)  "Chances Are"
6)  Eddie Fisher (8)  "Heart"
7)  Tony Bennett (7) "I Wanna Be Around"
7)  Sammy Davis Jr. (7)  "The Candy Man"
9)  Dean Martin (6)  "Everybody Loves Somebody"
9)  Steve Lawrence (6)  "Pretty Blue Eyes"
9)  Al Martino (6)  "I Love You Because"
12)  Guy Mitchell  (4)  "Singing The Blues"
12)  Frankie Laine (4)  "Moonlight Gambler"
12)  Tommy Edwards (4)  "It's All In The Game"
15)  Roy Hamilton (3)  "Unchained Melody"
15) Johnny Desmond  (3)  "The Yellow Rose Of Texas"
17)  Jack Jones  (2)  "Wives And Lovers"
17) Bing Crosby (2)  "True Love"
17)  Ed Ames (2)  "My Cup Runneth Over"
       (Ed did have 6 other Top 20 hits with the Ames Brothers)