Episodes to avoid:

Original Naruto:
26 (pointless re-cap aired with 27)
97
101 (Was about what's under Kakashi's Mask, could watch if you want)
142-147 (about Mizuki, had some cool action scenes with Asuma and Kurenai and some Iruka feels)
148-151 (cool mission with Team 8, HIGHLY recommend, but still filler)
152-157 (really cool arc with a former 7 ninja swordsman guy, also recommend)
158-177
178-183 (Cool story about the Village Hidden in the Stars)
184-202
203-207 (Feelsy story about Kurenai)
208-215


I left in fillers that were short or that were very good, will do the same for Shippuden.

Shippuden:
90-112 (Filler Arc about the 3 Tails, kind of cool but not needed)
170 and 171 (I have no idea why they thought putting 2 filler episodes in the middle of such an important and epic arc was a good idea)
176 is filler after 8 minutes
177 all filler
178 filler ends at 18:12 in
180 filler starts around 4 minutes in
181 filler starts around 3 minutes in
182-196
223-241
242 was filler, but it ties in with the upcoming canon episodes, and was pretty cool.
257-260 (This is all of Naruto up until this point summarized in 4 episodes, watch it if you want)
271 (Promotion for Road to Ninja, only watch it if you plan on watching the movie)
281
284 (Filler, but explained something about Sai that the manga left unexplained)
285 (Filler expanding on Pakura and her past)
286 and 287 (About how Tsunade and the Raikage first met)
289
303-305 (Filler, but about the Sound 4, kind of cool)
306
307 and 308 (Filler about Hayate)
309 and 310
311 (Prologue to Road to Ninja, would HIGHLY recommend you watch if you plan on watching the movie)
312-317
318 (About the past of the 8 tails and the previous Jinchuriki, kind of interesting)
319 (About Sasori)
320

List needs some further updating after this point.