Google Suggest is being gradually replaced with Google Instant in various parts of the world. At any rate, do the following:
- Go to Google.com (or your local version, or iGoogle) from any browser.
- Click the "Setting" link at the top right and select "Search Settings"
- Scroll down to the "Autocomplete" section and select "Do not provide query predictions in the search box."
- Click the "Save Preferences" button
You may have to repeat between browsers, as I believe the search preferences are saved to a cookie.
Update: since writing this, Google has change the settings page and now mine looks like this:
However, if you go to the Google SSL site (https://www.google.com) and select "search settings there, you'll see this option:
IMHO, if you turn these off and STILL get suggestions/instant - it's a bug that should be reported to Google (and remember, Instant was just launched a week ago, so give them time to fix their bugs).