Share your URL in an Email
If you want to send the URL of a Web page you’re viewing to a friend, tap the Address Bar, then tap Share. A new e-mail message, containing the URL, will open in Mail; just choose a recipient(s), add any comments you want to include, and tap Send.
Page Down
When not using a zoomed-in display, double-tap towards the bottom of the screen. The page will re-center around your tap. Make sure not to tap a link!
Jump to the top of the Page
Double-tap the very top of the screen, just below the time display to pop back to the top of the page. (Thanks John C)
Zoom onto a Single Picture
Double-tapping images in Safari zooms them to fit your iPhone display. If the picture is linked to a URL, this can prove a little tricky but it works great for non-linked images. Double-tap again to return to the unzoomed display. Using 2 fingers to double tap, and zoom a section of a web page will avoid the accidental clicking of links.
Zoom a Column
You can zoom text columns as well as pictures. Double-tap on the column to fit it to the display. Double-tap again to return out of the zoom. Not only does Safari zoom block-quoted text independently of regular text but if you move your finger after the first double-tap-to-fit, it interprets the next double-tap as a re-center page command rather than a return-to-previous-zoom. Smart.
Stopping a scroll
After flicking a page to get it to scroll, you can tap the page at any time to stop that movement. Don't forget, you can also manually drag the screen display to reset the part you're viewing.
Manual Zoom
This is probably one of the most-advertised Safari features (along with the flip-the-phone-on-its-side-trick) but it's worth mentioning again. To zoom into a Safari page, put your thumb and forefinger on the screen and move them apart. To zoom out, pinch the fingers together after starting with them apart.
Examining the URL
To peek at a link's destination, touch and hold the link for a few seconds. You can also do this with images to see if they are linked. If a link appears and you don't want to activate it, just slide your finger away until the destination text disappears.
Locking the Scroll to One Direction
The iPhone 'locks' your scroll to either vertical or horizontal only if the initial finger-slide is straight up/down or right/left enough. This can be very useful if you've got a skinny column of text with room on either side to get derailed. If not your initial scroll, using 2 fingers side by side will force vertical scrolling. Likewise 2 fingers stacked is horizontal.
Save Images
Save images in Safari by tapping and holding on the image and you will see a “Save Image” button. Great feature if you want to use images you find online as your wallpaper.
Press & Hold For Alternate Characters
Hold a letter for a popup of various versions of the character (i.e. to type España with the "ñ" simply hold "n" and simply slide/release to the appropriate character).
Click & Hold URL's
In Safari, hold a link to see the URL and site name.
Enter Special Characters in Safari Address Bar
When you have selected the number keypad (@123) while typing text in the Safari Address bar, pressing the Shift Key, changes the symbols you can select. In other keyboards (for example the Google search text box, the Shift key is replaced with a second symbol option key (#+=) but this doesn't appear in the address bar. To access these symbols, just press Shift key and pick the character.
Changing Search Engine to Yahoo
By default, Safari uses the Google search engine when you enter search text. However, you can change it to Yahoo but selecting the Safari Option in the Settings application. Pick this option and select the Search Engine option to change it to Yahoo.