I'm a fan of many of Google's contributions to the internet. Case in point: Google Maps. When they introduced this feature, I immediately forsook Yahoo Maps and Mapquest. Why? Because Google Maps was easier to use and more pleasing to look at. Now it even features satellite and hybrid views as well as measuring scale on each page. Apparently, lots of other people felt the same way. How did they show their love? By hacking it. But in good ways -- in ways that made what Google Maps does even better -- by combining various live and static data sets in Gmaps' geographical space. Some great examples:
HousingMaps = Gmaps + Nationwide rent/sell/sublet listings on Craigslist. I haven't used this yet to actually rent an apartment, but I can totally see the usefulness of it in terms of browsing within a certain neighborhood or radius.
Cheap Gas = Gmaps + Low gas prices pinned to particular filling stations.
GmapPedometer. Double-click out the twisty-turny route of your latest walk, jog or bike ride to find out how far you went.
Google Maps NYC-Subway Hack. Find out where exactly the train lines run and stop in relation to the streets above.
Entire blogs are written about the topic, too: Google Maps Mania.