Google Earth is all the rage, but Microsoft is trying to one up them with superior photos taken from helicopter's rather than Google Earth's satellite images. The Microsoft service is called Live Local although the link is local.live.com
You can either see an actual photo of the home or condo building you're interested in, or have fun and just type in a landmark like "golden gate bridge, san francisco, ca". You can switch between the crystal clear helicopter photos which are called "Bird's eye" view by clicking on "Aerial" which will take you to satellite images similar to Google Earth. Or while still in "Bird's eye" you can click on anyone of the 8 thumbnail photos to move in any of those 8 directions. Or click on the N, S, W, or E buttons to see different angles of the same property.
Finally, Live Local also lets you get driving directions, and switch to a regular map interface.
Unlike Google Earth you do not need to download anything, but you miss the fun of feeling like you are traveling from one destination to another. For all of the options, ease of use, and crystal clear photos, I'm a bigger fan of live.local.com. Use it in conjunction with my MLS Map search site SF-MLS-Search.com and you never have to leave your home to search for a new one. Add PropertyShark.com and Zillow.com and you'll find out just about everything else you want about any home. As a Realtor with MLS access I'll still have much more information to share with you, but you'll be able to do 80+% of the homework (or snooping around) with these free and fun internet tools.