Here’s a slick little online geographic tool called DishPointer. Enter your position (latitude/longitude), or your address, then select from a list of broadcast satellites in geosynchronous orbit. DishPointer will bring up a Google Maps display showing the proper orientation for your dish antenna for optimal reception from the selected satellite:
Check the box marked “Show obstacle”, and you can move the marker to show the maximum height an obstacle (like a tree or a neighbor’s house) can have without blocking your satellite dish’s line-of-sight view.
Click on the Google Earth icon, and have the line-of-sight to the satellite shown in 3 dimensions:
If your view of the satellite is blocked by terrain, that will be visible in Google Earth; if there are 3D buildings for your area, you’ll also be able to see whether your view is blocked by adjacent buildings as well.