If you are running the new 2.0 firmware on your iPhone or iPod touch, you might not have noticed a new handy shortcut in Safari. When you type in your address, hold down the ".com" button to get a selection of 3 other domain name endings: ".net," ".edu," and ".org." When you tap on any of the endings, it will be automatically inserted in the address.
Shame there’s currently no support for country specific domains such as .co.uk 🙁
As Kirsty mentions in the comments below, YOU CAN have .co.uk (and other country domains) – Here’s the instructions on how to set it up.