Google Earth (available for Windows, Mac & Linux) is an amazing tool. Its power lies in the overlays and 3D models, which users can create and share. A new blog, SinGeo, aims to be a resource for local overlays, 3D models and more.
For example, you can download a 3D model of the future Singapore Flyer. Or you might want to take a look at the Marina Bay Channel Development Plans. If you're a history buff, you might be interested in transposing a historical image of Boat Quay over Singapore at present (rather, close to present - GE's maps are slightly out of date). All in Google Earth, of course.
Aside from SinGeo, the Google Earth Community has a forum thread called Singapore, the Lion City. The first post in this discussion has a link to a constantly updated placemark file (version 4.7 at time of writing) which details almost every imaginable location in Singapore: schools, transportation, places of interest, etc.
If you aren't interested in installing Google Earth, but want to access aerial views of the earth quickly, check out Flash Earth. This flash-based mapping website allows you to quickly zoom to any point on earth. Also, you can toggle between various mapping service by Google, Microsoft, Yahoo and others. But you don't have support for overlays, 3D models and other nifty add-ons.
If you're interested in international Google Earth resources, check out the (unofficial) Google Earth Blog.
P.S. I just realised that my other post in Cool Stuff also involves Google. I can't help it if they make cool stuff!