Not one to be outdone by the myriad other net travel guides, Google today rolls out City Tours for planning and navigating itineraries.
Currently a Google Labs project, City Tours helps "identify points of interest and plan multi-day trips to most major-cities". To build your tour, just enter the destination city, and City Tours automatically maps out a three-day plan with around 10 activity suggestions per day. The site also suggests how long to spend at each place and clocks the walking distance between destinations. You can then manually add and remove sights, and change the date and length of your visit (up to a maximum of five days).
Given its Labs status, City Tours is still very much a work-in-progress. For example, though the site is decent at finding locations for large cities like London, it has a more difficult time doing the same for smaller cities. Also, estimated walking times aren't always accurate, which doesn't help if, say, you're trying to figure out whether to keep walking, pace yourself by grabbing a cab, or might actually need a rental car.
Check out the below link to test out City Tours for yourself, then let us know what else you'd like to see it (or any travel site) help you with.