1. YouTube video only: This is a very small script that eliminates everything on a YouTube page but the video itself.
2. Auto add to Google Reader: Bypass the page where you click "Add to Google Reader" or "Add to Google homepage" page and adds your desired feed right to your Google Reader.
3. Textarea Backup: Provides a backup of text you entered into text boxes in case of the event of a crash. Just go back to the page and the text will be there waiting for you. This one is great for bloggers or frequent commenters.
4. Googlenlarge: A great Greasemonkey script that allows you to hover over an image from a Google image search and an enlarged preview of the image will pop-up on the same page; Allowing you to preview any image search result without having to actually go to the page that contains the image.
5. Google Homepage Resizeable Columns: Pretty self explanatory; just click and drag in the white areas between the columns of your Google personal homepage and you can adjust the width of the columns.
6. Digg.com comment helper: A great digg script that highlights the most popular comments on a digg story. Perfect for finding those user-submitted links to mirrors or the extremely hilarious comments.
7. Digg.com washer: Another one for digg that allows you to add words that the script will then block the stories containing those words. Access the options for this one by clicking on the "Show Options" link on the digg front page right above the top story. You can also toggle the digg side bar on and off with this one.
8. Google Reader preview: This one will allow you to view the originating website for a story in one of your feeds. Just go on over to the "List View" and click on one of the stories.
9. Gmail macros: Adds some more keyboard shortcuts for gmail as well as allows you to create your own shortcuts.
10. Google Auto Pager: This is a great script that eliminates the need to keep hitting the "Next" button for some more Google search results. It automatically loads the next page's results at the end of your current page. It also works great with the Firefox extension Google Preview.

*Bonus script*
Pagerization: This one is just like the Google auto pager script, only it works on multiple search pages. It is a bit buggy still, however, but might be worth it to keep your eyes on this one.