If you've yet to try the service that allows you to search by Map - it's got a new and improved look. This screen shot is of San Francisco, and the mouse is hovering over one property so that you see it's basic details. If you then click it takes you to the Full Detail page.
You can use the criteria selectors on the bottom of the page to choose property types and price ranges. And then select portions of the map for area specific searches. Finally, you can Save Searches and set up auto-email alerts for those searches, and you can save specific properties to return to see what's happened with them. Try is out at www.SF-MLS-Search.com/welcome.html