You might have more processing plug-ins than you know what to do with, but can you honestly say that you know what effect each of them has on your music's sound? To help you learn, Auricula Software has released five 'ear training' plug-ins.
Available in Mac AU format, these go by the names of Helix, Helix Pro, Incus, Malleus and Staples. Load one of them it up and it'll automatically make an adjustment to your sound - you'll then be asked what you think this adjustment is.
The idea is that, by going through this Q&A process, you'll start to recognise how different processing techniques - EQ, filtering, delay, gain changes and alterations to the stereo field, for example - affect your music. Hopefully, the end result will be that you're a better producer.
All the plug-ins are available as demos - these can be downloaded from the Auricula Software website. If you think they could be useful, you can download the full versions for just $1.99 each ($8.99 for the full set).
At this price, they've got to be worth considering. These plug-ins might not make any sound, but if they give you a better understanding of how music production works, they could be immensely valuable.