A collection of websites I find useful to have handy.
Filehippo - A collection of free or trial software to download in one place. Most things you need a piece of software for you can find here. Also has an update checker that checks your software for security and other updates.
Zamzar - Covert a file type to another file for free and without having to install any software. Select the file, choose what to convert it to and Zamzar will email you when it is done.
Trend Housecall - Excellent online virus scanner. Works with IE and Firefox.
Mailinator - Avoid spam by using a temporary email address. Sites that require your email but you don't want to give it to them, give them a mailinator email address instead. Each mailbox can hold up to 10 messages.
AlternativeTo - Alternative suggestions when looking for a piece of software. Can't afford Photoshop? See what else can do the job and what people think of it.
Last.fm - Sign up to the site and tell it what bands you like and get your own personal radio station. Or alternatively, just listen to music for free.
What Should I Read Next? - Enjoyed a book? Put the title and author in to this search engine and it will give you a list of other titles you might enjoy.
Musicmagpie - Sell your unwanted CD's, DVD's and computer games. No bank details needed. Post them freepost and receive a cheque in return.