I'll try to keep this list maintained in the first post, tell me if any are offline.
- Ninite - Select and quickly install most common apps
- Allmyapps - Select and quickly install apps from a large apps list
- Dropbox - Store, Sync and share files online
- Speedtest - Test your internet speed
- Looking For Group - Funny adventure comics
- Downforeveryoneorjustforme - Check if a site is down for everyone or just for you
- Gnod - Search engine to discover new things
- Letter me later - Schedule your emails
- TinyURL - URL shortener
- X64-bit download - Find and download your 64-bit programs
- PolyCola - Search 2 search engines simultaneously
- Delicious - Manage, tag and share your bookmarks (and integrate with various apps)
- Mozilla Apps - Bunch of Mozilla apps like Firefox, Thunderbird, VirtualBox,..
- * "I don't understand" * - "I don't understand" in over 255 languages
- Google shell - Google tools from a unix shell in your browser, search, maps, wiki, etc
- Yahoo shell - Same as the Google shell, but for Yahoo
- StatusNet - The StatusNet platform enables communities, brands and organizations to incorporate micro messaging/blogging/sharing into their own domain.
- etherpad list - Edit a document together with someone else real time in your browser
- Url Shortener - Shorten a long url
- Google Translate - Translate a web page or text
- Printerfriendly - Make a webpage printerfriendly and customize it by cutting out parts or make a PDF of it
- Meebo - Sign in with MSN, Yahoo, AIM and Facebook at the same time on this website
- Slickdeals - Find some very good deals on this site
- Mailinator - Make yourself a temporary email and protect your good email address from spam
- drop.io - A realtime file sharing service
- Virscan - Scan a uploaded file with as much as 24(!) virus scanners
- WhatismyIP - What is your external IP address
- Aviary - Make your own image, video or music online without installing anything
- Devcheatsheet - Very nice cheat sheets for almost all programming languages
- Readability - Make your browser better readable
- Escapist magazine - Short and fun game/movie reviews
- Waybackmachine - Has millions of websites archived for lookup when a site is down
- Oldversion - Download old versions of applications for Windows/Mac
I will post some other of my favorite links here soon, feel free to post your own bookmarks here too!