The PowerShell community has published many modules for PowerShell, head over to PowerShell Gallery | Home to see what has been done. Personally I have not used any modules as I like to learn and write stuff myself, however I should really use modules as people have spent a lot of time and effort on some of these. Below is a list of modules I have come across that look useful, even if I have not used them. The list is partly a collection for my reference but also something that might help others.
Clearly you use these at your own risk and you should asses them first.