Google launched a tool that offers suggestions as you type "Google Scribe," that "provides text completion service. Using information from what you've already typed in a document, Google Scribe provides related word or phrase completion suggestions. In addition to saving keystrokes, Google Scribe's suggestions indicate correct or popular phrases to use," explains Google.
If you don't like to see suggestions for all the words you type, enable the on-demand mode (Ctrl+Shift+J) and you'll only see suggestions when you press Tab.
To use this tool, you can just add a bookmarklet to your browser and use Google Scribe in Gmail, Blogger, Google Docs or on any web page that includes text fields.
[Source: Thanks, Alex]