Found this recently and thought there were some nifty tools featured there. (From what I can deduce, this is merely a compendium of tools. They aren’t necessarily the creators of them. I think more than one entities efforts are included. Because of that some of them appear to overlap in abilities.) Scrolling down each one a ways reveals some more info, known problems, end users advice, etc.
Radius Around Point - ie, what area falls within say a 50 mile radius of a particular location. Size of radius can be set to any desired distance.
How Far Can I Travel - how far can you travel within a certain time period given a specified mode of transportation and speed travelled.
How Far Is It Between - gives both an “as the crow flies” and roadway distance between two named points on a map.
Trip Calculator - Similar to the above tool, but allows you to determine the route as opposed to an algorithm determinining the most direct route. Want to meander along on back country roads and take a more circuitous route? This will allow you to figure out the distance and time involved.
Measure Distance - (Perhaps somewhat similar to the above.) You can do a very precise measurement of the distance of a route you want to or have traveled. And you aren’t limited to an “as the crow flies” route either. You can click and leave a way point as many times as you like to more accurately follow the route you will or have taken.
KML File Creator - Keyhole Markup Language. uhm....not entirely sure what this does.
Area Calculator - A planimeter tool that can measure the enclosed area of a defined polyline on a map. Will also give you the perimeter length as well as the area in a few different formats.
Map Tunneling Tool - A bit silly, but allows you to determine where exactly you would end up on the other side of the Earth - if you were to dig a tunnel straight through from where you are.
Tunnel to the Other Side of the Google Earth - Similar to the above tool.
How Far Does Santa Have To Travel - Again, another bit of silliness.
International Meeting Centre of Gravity Tool - Have a bunch of delegates from many different locations coming together for a conference, meeting, etc.? This tool will allow you to determine the most central location to meet.
Range Finder - Find out the end point on a map when you specify a start point, a bearing and a distance.
Elevation Finder - Used to find an estimate for the elevation of a point on the earth. Although it didn’t display any info for me. Maybe just the particular browser I used?
Find Sunrise and Sunset Time at a Location - Find out the next sunrise and sunset of any point on the earth.
There are also some post code and zip code related tools.