The early Hanna-Barbera shows are timeless. Most of the characters were designed by Ed Benedict as work-for-hire, and they were instrumental in making HB an animation powerhouse that would go on producing hundreds of shows well into the 90's.
Ranking very high among my favorite shows of all time is one of those, Top Cat. The writing and voice acting are just stellar, and even the HB brand of limited animation seemed to work with TC's often misfiring schemes, which (disregarding the dated P.D. telephone gags, of course) are still very enjoyable. Not bad for a 50 year old cartoon primetime series.
Here's a quicky I made in Char Design class when discussing our earliest influences: