PBJ Otter, Little Bear, Rollie Pollie Ollie, and Franklin-which i still watch when i see it on XD actually if i see any of these shows on i'll probably watch it, but i have only seen franklin still on air(not the remake of it x_x)
I loved Little Bear. I also loved this show about anthropomorphic beavers who talked about folktales. I can't remember the name of it. My brother loved the teletubbies, and as unabashed of an Anglophile as I am, that is still one incredibly weird show.
As a little kid, I liked Blue's Clues and I don't really know what else there was that I really enjoyed on Nick Jr.
Backyardigans is crazy underrated and the five main characters are almost literally the only characters in the show, making it really enriching and cerebral when they change costumes and portray themselves as different characters. It is actually enriching in ways that are not blatantly "educational" like Dora and Diego.
Max and Ruby is legitimately funny and cute, and the mild antics never get old. Olivia is a sort of show, with icky CG, that is trying to take some of Max and Ruby's thunder.
I have a history of living with toddlers and little kids.
When these channels first came out (here in Australia at least) I think I was at that age where I was just a bit too old for anything on Nick Jr but still plenty young enough to watch Nickelodeon for many more years (without getting questioned on it ).
But I suppose Nick Jr had some more...bearable "kiddy" cartoons at the time which I watched anyway when there was nothing else on. Best one I remember was "Franklin". That was one infants cartoon that wasn't completely retarded As for Nickelodeon itself, my favourite pre-Spongebob cartoon was "Aaaaah! Real Monsters!"