SubLab by FAW is a very intuitive plugin that takes kick drums and turns them into some of the heaviest and deepest sub-basses that are sure to get your speakers shaking.

CA2600 by Cherry Audio is a great introduction into semi-normalled patch cabling, meaning this synth works with or without patch cables.

Reference 2 by Mastering The Mix is a comprehensive analysis tool that is focused on referencing audio tracks. Comparing your music to that of others is crucial in nailing a good mixdown and master.