I'm going to start watching One Piece from the beginning. I found the following guide to what's filler and what's not. Any particular filler I should watch and any I should absolutely avoid?
http://www.animefillerlist.com/shows/one-piece
You can watch 50 and 51. 51 is a little dumb, but 50 is based on stuff that Oda wanted to include in the manga but had to cut in order to keep pace with where he wanted the manga to be (he wanted the Straw Hats reaching the Grand Line in chapter 100).
101 has some very important canon material in the late parts of it (but the rest of the episode is quite terrible). 102 is an episode I've always honestly kind of liked.
196-206 is the G8 Arc. If you know it's filler, it's recognizable as such, but it's pretty entertaining on its own. WATCH.
213-216 is part of Davy Back Fight. As you might remember, it's pretty integral to the way the anime handled Davy Back Fight, unfortunately.
220-226 is Ocean's Dream, 279-283 is the Enies Lobby recaps, 291-292 and 303 are all Boss Luffy, 317-319 are those terrible Water 7 episodes, and you just experienced 326-336.
382 and 383 are pretty terrible, but they do have
, if you're into that sorta thing. 384 is a pretty solid little
-centric episode.
406-407 is more Boss Luffy.
426-429 is the actual worst. Watch at your own peril.
457-458 is time wasting recaps/stalling for time.
492 is the second half of a two-parter that includes Toriko episode 1. Skip. Debatable if it will ever even be made (legally) available in the US.
497-499 is an expansion of a particular arc. Pure filler, but not the worst. Easily skippable, but also watchable.
506 is a fleshing out of some canon things, even if they're technically filler in that they didn't all appear in the manga. WATCH.
542 is another Toriko episode. Skip.
575-578 is another movie based filler arc. Not as bad as 426-429, but very skippable.
590 is yet another Toriko episode, this time also crossing over with DBZ.
626-628 is another really really awful little mini arc. Skip.
653 isn't really a filler episode. It has a lot of filler in it, but not entirely, and it's part of a canon arc.