There are 3 ways to access Google without visiting its homepage. You can install the Google Toolbar but it takes some desktop real estate and I don't believe you can access it from the keyboard. 2nd is by using the quick search within Firefox (top right, access shortcut is Ctrl-K). The 3rd one is using Firefox's Keyword Search. I use this last method a lot: from Firefox, F6 brings focus to the address bar and i start my Google query with g before hitting enter

Search
Simple search using Google, nothing revolutionary
bloc party matt tong asian
flickr redesign

Site Search
Restrict search within a site (domain)
site:charlierose.com "deep throat"
site:threadless.com elephant

Spell check and definition
Check spelling quickly. Bonus: link to a definition from Answers.com which has basically usurped Dictionary.com in my mind for definition because of its placement within Google results
haagen dasz (Did you mean: haagen dazs)

Package Tracking
This is and old trick and of course, usefulness depends on how much you ship (or purchase online), currently supports USPS, Fedex and UPS (where's the love for DHL?). I read you can simply enter the tracking number but prefixing with the shipper name has been more reliable for me
usps 03043490000020963791

Unit Conversion
Not used all that often but every now and then I still have to do some US to metric unit conversions
6 miles in km (6 miles = 9.656064 kilometers)

Weather
Straight forward, format: weather zip or weather city state
weather 95134

Search History Notes
Since I started using Google's Search History (as in right click, copy link location in Firefox), Google now appends a code to track what results I click on so copying the URLs become kinda tricky, you get stuff like http://www.google.com/url?sa=U&start=1&q=http%3A//www.blocpa.. instead of http://www.blocparty.com. Google also returns time stamp of last visit and visit count within its search results

More to explore
Froogle, Movies, etc

Google Maps
Google Maps has been real hot since its release in Feb 2005, I assigned the letter m for its Firefox Keyword Search

Maps
Enter the zip if you know it instead of city, state
170 west tasman dr, 95134

Directions
Use from and to keywords
from 95131 to san francisco, ca

Business Directory (address and phone)
Name followed by city, state or zip. Uses data from the local.google.com, works off and on, I often have to go to local.yahoo.com (the directory information actually shows up using regular Google too but I like seeing the results displayed on a map)
a16 san francisco ca