You can download the full Ultimate edition and use it without a key for 30 days to test out all features [2].
You can download "EAP" builds for free. These are pre-release versions of the software that allow you to use the latest features in exchange for helping JetBrains find bugs [5]. IntelliJ IDEA Serial Key Download HERE
If you have a valid university email or ID, JetBrains provides the Ultimate edition for free via their Educational Licenses program [3]. You can download the full Ultimate edition and