Since 2006, the Eclipse Foundation has coordinated an annual Simultaneous Release. Each release includes the Eclipse Platform as well as a number of other Eclipse projects. So far, each Simultaneous Release has occurred on the fourth Wednesday of June.
Eclipse Indigo corresponds to platform version 3.7, while Eclipse Juno - to platform version 4.2. Juno has a lot of improvements on the UI, but this results in a bit slower performance that the previous versions. Personally, I would prefer using Indigo rather than using Juno.