We are already using Redmine internally for issue tracking.
Now we also need to track the inventory and maintenance history of equipments of a customer (which should be able to connect and change the state/location of their equipment).
Which Redmine plugins would you recommend for this purpose?
I don't know your exact requirements but you may find the following plugins helpful. You may build your own plugin on top of these with some customization as per your requirements so that its compatible with the latest version of Redmine.
http://www.redmine.org/projects/redmine/wiki/PluginEzlibrarian