truly amazing and extremely useful

http://www.google.com/glm

This is Google's map site, but for your Java-enabled phone. You can even use the satellite mapping feature, and get directions. Except for any carrier-related charges, this should be free if you have web minutes in your plan.

If you visit the site above on your computer, it will walk you through your carrier and phone model choice, and send a text message to your phone with the same link. If you just visit the link with your phone, then you'll get to download the pretty small Java applet.

I think Verizon is the only major service not covered. Hopefully, your phone is Java enabled.

You already knew about Google's awesome mapping feature, right?

http://maps.google.com

I wish it would hook up to the GPS-like features that some phones have and automatically show your current location, but this is Google, and I'm sure that feature is next.

There are websites which have combined the Google satellite mapping to traffic reports. It would be really neat to be able to get that kind of mapping as well, but it might be too much to ask for on a phone.