Google toolbar is a free tool which lets you search from any Web site without returning to the Google home page to begin another search. You can customize your search to include just the site that you're visiting, or just the page you're viewing. You can also use the toolbar to find similar pages, or sites that link back to that page. Google tolbar has provided very remarkable features like: "Google Suggest" query suggestions (available in Firefox only), a pop-up blocker, a WordTranslator, SpellCheck and AutoFill functions.

Google Toolbar Features- IE Toolbar Version 4

New! Enhanced Search Box
As you type a search query into the new Toolbar's search box, you'll see a list of useful suggestions based on popular Google searches, spelling corrections and your own Toolbar search history and bookmarks. You can also click the 'G' icon in the search box to search different Google sites, the current site, or sites for which you've installed custom search buttons.

New! Custom Buttons
You can add buttons to your Toolbar that will let you visit and search your favorite websites and keep up with interesting feeds. Button Gallery offers a selection of ready-made buttons for popular sites, and you can make your own buttons in seconds by right-clicking within the search box on any site and selecting "Generate Custom Search..."

New! Bookmarks
Want to create and label bookmarks that you can access from any computer? Simply click the Toolbar's star icon, or right-click the star to add and label a bookmark. You'll be able to access your Bookmarks menu on any computer with the new Google Toolbar installed.

Note: this feature stores your bookmarks online, so you&'ll need to have a Google Account and be signed in to create and access your bookmarks. You can also view your bookmarks using your Google Account&'s Search History feature. Just click the "Search History" link that appears in the upper right-hand corner of the Google homepage when you&'re logged into your Google Account and you&'ll see your Bookmarks.

New! Send To
You can use your Google Toolbar to share web pages via email, text message (SMS), or blog. To share an entire page, select from the Toolbar&'s "Send To" menu; to share an excerpt, simply select the section of the page you want to share before clicking "Send To."

Note: sending text messages via the Google Toolbar is free. Your cell phone carrier, however, may charge a fee to receive messages, on either a monthly or per-message basis.

New! Google Account Sign-in
Your Google Account is your access point for Google services like Personalized Homepage, Google Groups and Gmail – and now you can sign in and out right from your Toolbar. Simply click on the Settings button on the right end of the Toolbar and select "Sign In" (you&'ll know you&'re signed in when the Toolbar shows you a green light).

AutoFill
Tired of typing in your address and credit card information every time you shop online? AutoFill makes shopping a breeze by enabling you to fill out web forms with a single click. Just enter your info once in the Toolbar's Options dialog box and you're ready for an online shopping spree. (Note:your credit card info stays password-protected.)

AutoLink
The online review of a great new restaurant has the place's address but no map. You could type the restaurant's street, city, and ZIP code into the search box, but why bother, when clicking the Toolbar's AutoLink button will automatically create a link to an online map (US addresses only)? AutoLink can also link package tracking numbers to delivery status, VIN numbers (US) to vehicle history, and publication ISBN numbers to Amazon.com listings.

Translate
Ever need to translate non-English web pages into English? Just select "Translate this page" from the Toolbar&'s Translate menu to view French, German, Italian, Portuguese, Spanish, Chinese (Simplified), Japanese, and Korean pages in English.

You can use the WordTranslator feature to translate English words on a web page into another language. Select "Enable WordTranslator" from the Translate menu, then simply hover your mouse cursor over an English word to view its translation. WordTranslator supports translation from English into French, German, Italian, Spanish, Chinese (Traditional and Simplified), Japanese, and Korean.

Address Bar Browse by Name
Browse by Name helps you find a site even when you don't know its URL. Just type the site name into your browser address bar, and Toolbar will take you there automatically. For instance, try typing "oxford" into the address bar to go directly to the university's home page at www.ox.ac.uk.

If you type in something that doesn't have an official home page, like "digital cameras," Browse by Name will automatically show you search results for that term.

Pop-up Blocker
Lost in a jungle of annoying pop-up ads? Toolbar's pop-up blocker keeps your screen free and clear.

SpellCheck
ARe yu a raelly bad tyipsst? Google Toolbar's new SpellCheck button finds any spelling mistakes whenever you type into a web form, including web-based email, discussion forums, and even intranet web applications. The AutoFix option even corrects all of your text with a single click.

PageRank Display
Wondering whether a new website is worth your time? Use the Toolbar's PageRank™ display to tell you how Google's algorithms assess the importance of the page you're viewing.

Highlight Search Terms
Once you've used the Google Toolbar to find a web page, there's no need to scroll around looking for your search terms. The Highlight button instantly lights them up on the page, making it easier to find relevant information.

Word Find Buttons
Finding a particular word on a web page can be frustrating. With the Google Toolbar however you easily jump to the first instance of a word by typing it into the Toolbar search box, then clicking on the Toolbar's Word Find button to find each additional occurrence of the word.

Auto Update
There's no need to check for new versions of Google Toolbar; updates are installed automatically, so you'll always have the latest and greatest version.

Reference:

http://www.google.com/support/toolbar/bin/static.py?page=features.html&v=4