Ok...of course the classics...Bugs et. al., most of the old Hanna Barbera cartoons, Rocky & Bulwinkle. (I remember the old casper too LordKat

) Animaniacs is newer than those, but was ok too.
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I haven't watched most of the classics in a while though...for the same reason that I don't read 'Peanuts' or 'Blondie' or 'Beetle Bailey' in the newspaper anymore. You can only do the same joke so many times before it becomes tired. Of course, I'm one of those people who can quote most of a movie after I've seen it once...so multiple viewings can get a bit boring.
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Favorite? If we're going old school, then I'll throw out these:
"Peter and the Wolf" (Composed by Sergei Prokofiev and narrated by Sterling Holloway (an old bit part actor, most famous for being voice of Winnie the Pooh)) and
"The Whale who Wanted to sing at the Met" (Voiced/sung by Nelson Eddy).
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Newer cartoons? I'm not big on most of the American cartoons from the last couple of decades. Though
Southpark's "Make Love, Not Warcraft" is hilarious(How do you kill that which has no life?)...even if it does get a bit too crude at times. Totally reminds me of my WOW addicted younger brother though.
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For newer cartoons, I actually perfer anime. My favorites tend to have well developed characters, are relatively well drawn, and have good music.
Utawarerumono and
Inuyasha were probably the best all-around in all three categories. Even if some of the episodes of Inuyasha were a bit juvenile at times, overall it was a good series (with musical themes for each character much like Peter and the Wolf).