Shortwave

Shortwave is a nifty tool that can save you a few page loads. When clicked, it pops up a command window that allows you to enter shortcuts. For example, "yt some search term" will open the youtube search results page for "some search term." This is nice, as it prevents you from having to load the youtube home page first. The really cool part is that the shortcuts are cutomizeable.

Here's a screenshot of the bookmarklet in action:

Fullscreen Youtube

This bookmarklet opens up any youtube video in fullscreen mode. Tested.

http://trainque.com/blog/2008/07/25/bookmarklet-view-youtube-in-fullscreen-mode/

XRAY

http://www.westciv.com/xray/

This is a cool bookmarklet that quickly gives you a TON of info about any element in a page.

Here's a screenshot:

YUI Logger Bookmarklet

Use this bookmarklet to pop up a YUI logger window for help with debugging javascript code:
http://blog.rajatpandit.com/sandbox/yuilogger/index.html

Clicking this bookmarklet will cause this debugger window to appear on your screen:

Subscribe in Google Reader

Here's a gem from dailyapps.net.  This bookmarklet lets you subscribe to feeds in Google Reader. 

Subscribe in Google Reader <-- (actual bookmarklet -- drag this to your toolbar to install it).

Evernote Bookmarklet

I've been using the new Evernote bookmarklet for the past few days.  It does a fairly good job of capturing a page and storing it in evernote, although it works much better in Firefox than in Safari.  Here's some more info from the Evernote blog:

http://blog.evernote.com/2008/06/26/web-clipping/

A Better TinyURL Bookmarklet

Kim Scarborough has posted a bookmarklet for TinyURL that handles anchors within pages.

http://kim.scarborough.chicago.il.us/do/sites/blog/2008/06#a-better-tinyurl-bookmarklet

I tested it and it worked quite well with Wikipedia.

http://tinyurl.com/3o3wuw