Wikipedia lists 63 Nick shows from the 90s:
http://en.wikipedia.org/wiki/Category:1990s_Nickelodeon_shows
Of those I am most fond of (in no particular order):
The Adventures of Pete & Pete
The Angry Peavers
Are you Afraid of the Dark?
Doug
Nickelodeon GUTS
Hey Arnold!
Kenan & Kel
Legends of the Hidden Temple
Nick Arcade
Rugrats
Wild and Crazy Kids
Honorable Mentions:
Figure It Out
KaBlam!
Rocko's Modern Life
Secret World of Alex Mack
What would you do?
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Eff_Dee
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