By your title, I'm assuming we're leaving out solo artists?
Top 10 frontmen:
1. David Lee Roth- Van Halen
2. Freddie Mercury- Queen
3. Robert Plant- Led Zeppelin
4. Phil Lynott- Thin Lizzy
5. Bono- U2
6. Steven Tyler- Aerosmith
7. Ronnie James Dio- Rainbow and Black Sabbath
8. Ray Davies- The Kinks
9. Mick Jagger- Rolling Stones
10. Lou Gramm- Foreigner
Top 10 frontwomen:
1. Grace Slick- Jefferson Airplane/Starship (but NOT Starship without Jefferson in front of the name)
2. Joan Jett- And The Blackhearts
3. Shirley Manson- Garbage
4. Stevie Nicks- Fleetwood Mac
5. Chrissie Hynde- The Pretenders
6. Diana Ross- The Supremes
7. Ann Wilson- Heart
8. Nancy Wilson- Heart (yeah, I cheated, so what?

)
9. Debbie Harry- Blondie
10. Belinda Carlisle- The Go-Gos