From Google Suggest FAQ - "As you type into the search box, Google Suggest guesses what you're typing and offers suggestions in real time. This is similar to Google's "Did you mean?" feature that offers alternative spellings for your query after you search, except that it works in real time. For example, if you type "bass," Google Suggest might offer a list of refinements that include "bass fishing" or "bass guitar." Similarly, if you type in only part of a word, like "prog," Google Suggest might offer you refinements like "programming," "programming languages," "progesterone," or "progressive." You can choose one by scrolling up or down the list with the arrow keys or mouse."
Google offer this Suggestion tool through several Google services and can be used by downloading the new version of Google Toolbar.
From this today morning I have found that Google Suggestion on our search keywords are available there from the Google homepage itself which was not there by default. Actually Google just announced they will start to roll out Google Suggest as a default feature for the Google.com homepage over the next week. This feature will reduce your time and brainstorming to get the best results with the best keywords and phrases. It also reduces your spelling errors and saves keystrokes.