Google Maps, Yahoo Maps, Mapquest, Ask Maps and Microsoft Windows Live Local all have good features.

One reviewer found that Yahoo Maps was the best service, hands down. (Yahoo covers only the USA and Canada.)

TechCrunch » Comparing the Mapping Services

Personally I am more interested in Google Earth, software you need to download to your computer. It is a novelty now, but as resolution improves world wide, it will be fantastic.