I've just been to a talk by Chris Aniszczyk. It was a great talk about Plugin-Development with cool tips and tricks.
So things I need to remember for my next RCP work:
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Plugin-Spy: A great way to find out anything about my current plugin. This should be especially useful if you are looking into a RCP-App that you haven't developed or you just don't remember everything. 
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BundleClassloader.loadClass(): A great debug-point to figure out Classloader-problems 
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Core-Tools: Small utilities for Plugin-Development: 
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Memory Analyzer (MAT) Their is Eclipse based Java heap analyzer by SAP