All these episode's are Filler's and this list will be updated monthly!! XD If one of the episodes aren't a filler please message me so I will correct it! XD
Episode: 54-60 (61- Half Filler)
Episode: 493-504 (505 Half Filler)
A friend started watching the series I wanted to dig up a list of fillers to skip. I also double-checked on an episode name list as to what all crap was being passed.. This list is good but as Jroflcopter pointed out, 493-504 is new stuff about Luffy's past.
Also, 453-458 are based on the cover pages of the manga, so they're filler-like side stories. For other, earlier examples you have the side-adventures of Buggy and Coby + Helmeppo, which you didn't list as filler. All the side stories are plot-relevant anyhow and do get referenced.