SafariRestore from SweetP Productions does one simple task: It lets you save all your open tabs for recovery later. Click the "SafariRestore" button in the Safari toolbar, and you are offered the option to save your current session or restore a previous session.
True, Safari does have the built-in ability to save multiple tabs as bookmarks (right-click on the tab bar and select the Add Bookmark for These Tabs option), but SafariRestore lets you save and restore groups of tabs without creating permanent bookmarks for them.
You can save up to six sessions; the most recent will be opened automatically the next time you start Safari. Create several sessions for different tasks -- a social networking session, a project management session, a business research session -- and switch back and forth over the course of the day.
Duplicate Tab Button
This extension from Thiemo adds a button to create a new tab with the same Web page displayed as in the current tab -- useful if you want to keep a site open and still be able to surf away. You can also designate whether the new tab is a background or foreground tab by default in the extension's preferences. It's a useful addition to Safari's built-in ability to open links in new tabs by right-clicking or by holding the Command key down while clicking.
This extension from Amberlight installs a bar below the address and bookmarks bars that can provide a variety of information -- current weather, date/time, various world clocks and an RSS feed in a news ticker format. (You can customize the display in the extension's preferences.) While it duplicates the functionality of some Mac OS X Dashboard widgets, it does so in an always-visible format.
Ultimate Status Bar
Safari's built-in status bar (at the very bottom of the browser window) is rather Spartan, showing you destination URLs for Web links and page-download status and not much else. Interclue's Ultimate Status Bar offers more functionality and customization. When you roll over links on a Web page, the Ultimate Status Bar can show you favicons (if available) for the destination Web pages, expanded URLs of shortened links, and file sizes for non-Web-page links such as PDFs, compressed content or disk images.
If you have Safari set to display its default status bar, the Ultimate Status Bar appears just above it; if you toggle Safari's status bar off, Ultimate Status Bar replaces it. The bar can be customized using various color themes, and it automatically disappears when not in use.
Productive computer users know that the less often you have to shift your hands from the keyboard to the mouse, and vice versa, the more efficiently you can work.
KeyStroke from solusHex enables a range of keyboard shortcuts in Safari, allowing you to scroll up and down, return to a previous page, zoom in and out, and perform other functions using single keys (such as "j" and "k" to scroll down and up, respectively -- a shortcut familiar to Gmail and Google Reader users). You can reassign each function to any key you like if the defaults don't make sense to you.
If you're more comfortable with the mouse than the keyboard, you might prefer Kai Straßmann's MouseGestures extension. It lets you assign actions such as "back" and "close tab" to four gestures (up, down, left and right) you make with your mouse.
To trigger a gesture, hold down the mouse button you designate in the options (typically the right or middle button) and sweep the mouse up, down, left or right. You can execute common navigational functions much more quickly with a gesture, so you can focus on getting your work done.