Which episodes of the Naruto anime are core plot and which are filler? For both the original Naruto series and Shippuuden, which episodes should I watch if I want to avoid the filler? I'm only interested in core plot and character developments.

To make this question a bit more concrete: Which episodes are directly based off the manga, and which were produced with unique content for only the anime? At what points did the anime "catch up" to the manga and require non-manga-related content to continue airing episodes while the manga produced new content?
The Naruto anime is broken up into two "Series". The first is Naruto, which covers events up until the 3 year time jump in the manga. The second is Naruto: Shippūden, which starts after that jump and continues onwards. Both series have a fair share of anime exclusive plots, so here's the breakdown of Anime exclusive plots:

Naruto


Ep 26: "Special Report: Live From the Forest of Death" - Summary Episode
Ep 102 - 106: "Land of Tea" Arc
Ep 136 - 219-ish (This is where they let the Manga truck along a lot)


Ep 136 - 141: "Land of Rice Fields" Arc
Ep 142 - 147: "Mizuki Strikes Back" Arc
Ep 148 - 151: "Search for the Bikōchū" Arc
Ep 152 - 157: "Curry of Life" Arc
Ep 158: "Follow My Lead! The Great Survival Challenge"
Ep 159 &amp; 160: "Bounty Hunter" Arc
Ep 161: "The Appearance of Strange Visitors"
Ep 162 - 167: "Land of Birds" Arc
Ep 168: "Remembrance: The Lost Page"
Ep 169 - 173: "Land of Sea" Arc
Ep 174: "Impossible! Celebrity Ninja Art: Money Style Jutsu!"
Ep 175 &amp; 176: "Imposter" Arc
Ep 177: "Please, Mr. Postman!"
Ep 178 - 183: "Hoshigakure" Arc
Ep 184: "Kiba's Long Day"
Ep 185: "A Legend from the Hidden Leaf: The Onbaa!"
Ep 186: "Laughing Shino"
Ep 187 - 191: "Land of Vegetables" Arc
Ep 192: "Ino Screams! Chubby Paradise!"
Ep 193: "Viva Dojo Challenge! Youth is All About Passion!"
Ep 194: "The Mysterious Curse of the Haunted Castle"
Ep 195 &amp; 196: "Third Giant Beast" Arc
Ep 197 - 201: "Trap Master" Arc
Ep 202: "The Top 5 Ninja Battles!" Recap Episode
Ep 203 - 207: "Kurama Clan" Arc
Ep 208: "The Supposed Sealed Ability"
Ep 209 - 212: "Shinobazu" Arc
Ep 213 - 215: "Menma" Arc
Ep 216 - 219/20: "Ultimate Weapon" Arc - Note that 220 is part of this arc, but also includes some canon when




   Naruto and Jiraiya leave the village for training, and others begin training as well


Naruto: Shippūden


Ep 54 - 71: "Twelve Guardians Ninja" Arc
Ep 90 - 112: "Three Tails" Arc
Ep 144 - 151: "Tsuchigumo Kinjutsu" Arc
Ep 176 - 196: "Konoha History" Arc
Ep 222 - 242: "Adventures at Sea" Arc
Ep 290 - 295: "Chikara" Arc 500 Episodes (total) celebration
Ep 303 - 320: From the "Shinobi World War" Arc
Ep 327: "Nine-Tails"
Ep 347-361: "Shadow of the ANBU" arc
Ep 376 - 377: "Mecha Naruto" arc
Ep 386: "I'm Always Watching"
Ep 388: "My First Friend"
Ep 389-390: "Hanabi Flashback"
Ep 394-423: "Chunin Exam" arc
Ep 416: "The Formation of Team Minato"
Ep 417: "You’ll Be My Backup"
Ep 419: "Papa's Youth"
Ep 422-423: "Konohamaru's training" arc


Also of note is the Kakashi backstory "Kakashi Gaiden" is shown in the Shippūden (Ep 119 - 120), which is out of order as to how it appeared in the Manga (Chp 239 - 244). In the manga, it was between what became the first and second series (the time jump).

Additionally, none of the movies are based on Manga plots.

Source for most of this information was the Naruto Wiki. "Shadow of ANBU" info from Naruto HQ