I guess the term 'old skool' is relative to your age. I'm 35, so for me, it's 80's and very early 90's. A few memorable ones for me:

The obvious:

Run DMC
Eric B and Rakim (who had a smoother voice and delivery than Rakim?)
Biz Markie (imo)
The Fat Boys (yea, kind of a joke but I liked em' back in 83' lol)

Some of my favs:

Master Ace (before he was 'Masta' Ace)
Ed OG and da Bulldogs
D-Nice
Main Source
Leaders of the New School (well, at the time it was considered new school lol)
Das Efx
Fu Schnicken
Gangstarr
Kool G Rap and DJ Polo
The Ghetto Boys
A Tribe Called Quest
Brand Nubian
Wu Tang
Lords of the Underground
The Jungle Brothers
EPMD
Redman
X-Clan


As I think back and remember others, i'll update. Give me yours - and please keep 2000 and later shit OUT of this thread!