This is my favorite temple - gardens of all the ones I have visited before. I visited the Temple of Heaven last August 18, 2008.
Upon further reading, this is actually the largest heaven worship architectural complex in the world. The Temple of heaven or Tientan covers an area of 273 hectares, but the main buildings cover only one percent of the whole layout. That means you would do a lot of walking when you are inside just to get to all of the main temples. A through ticket costs Y35 and would give you access to all the main buildings.
These are Hall of Prayer for Good Harvests, the Imperial Vault of Heaven with its Echo Wall, and the Circular Mound Altar.
Hall of Prayer for Good Harvest
Imperial Vault of Heaven and Echo Wall
Circular Mound Altar
Nine Dragon Juniper