I've gathered for you a list of what I believe are the world's best bookmarklets – the ones I've found most useful and probably couldn't continue without. They appear as links; to use them, simply click and drag them onto your browser interface. I tend to keep mine just under my address bar.
frmget – Many web-driven applications accept input in the form of GET variables as opposed to POST variables, despite defaulting to the POST method. By using this button to convert POST forms to GET forms, variables are modifiable in the Address Bar and search results often become bookmarkable where they were not before.
remove maxlength – Ever start typing in a text box only to find that the websites's author set a limit on the text length for no good reason? This button will remove those annoying limits and will allow you to type as much text as you like. I often find this very useful. However, this will not help you when the text length is checked on the server-side.
show hiddens – This bookmarklet will turn all hidden variables into modifiable (and labeled) textboxes. This often comes in handy when you want to see (or change) what data is secretly being passed, without having to sift through the page's source.
view passwords – Are your remembered passwords being sent to your browser in plaintext every time you go to login? Use this button to reveal the content of those masked password boxes.
undisable – Have you ever wondered what would happen if you somehow click those greyed out checkboxes or buttons somehow, even though they're greyed out? Find out by clicking this one first. It will undisable/enable all elements on the page including check boxes, radio buttons, text boxes, and just about anything else that would otherwise be disabled.
toggle checkboxes – Toggle (check or uncheck) all of the checkboxes on a page at once.
Alexa – Check the Alexa ranking of any site with a single click.
zap style sheets – Find out what the page you're on would look like without any Cascading Style Sheets
YSE – Explore other indexed content on a site without having to follow all the links with the Yahoo! Site Explorer
Y – Find out what pages link to the one you're looking at (according to Yahoo!)
MS – Find out what pages link to the one you're looking at (according to MSN)
Please keep in mind that I didn't create any of these bookmarklets. They came from of the following places, which are great places to find more:
Jesse's Bookmarklets Site
Steve Kangas's Bookmarklets.com