While previously mentioned Readability is king among article decluttering bookmarklets, NotForest is a great alternative that provides super-clean pages, while also adding a few font options on the article page itself, so you can tweak pages on a per-article basis.
Readability is great, but it annoys me that I have to choose my font type and colour when I create my bookmarklet—I'd rather choose them on an article-by-article basis. That way, when I'm reading at night, I can quickly switch to white-on-black text, while keeping things black-on-white during the day. NotForest adds these options to the articles, so you don't have to create multiple bookmarks (or conform to one style).
I also found that, while it didn't do a great job of grabbing pictures from the original article (which is often not a big deal), it did a better job than Readability of cleaning up some pages. Where Readability would poorly reformat links from the sidebars and bottom of a page (New York Times articles are a good example), NotForest would give me just the article—no more, no less. If you like the idea of readable text but aren't a huge fan of Readability's implementation, NotForest is a great alternative. Hit the link below to check it out.