I would not recommend making a list of most common modules and importing them in all your applications just because they are widely used. Most modules use external libraries and can cause issues when they use different versions of the same library. Also some modules have outdated libraries which come with security risks.
I would recommend to import a module into your app when you have a use for it.
Very usefull for most projects:
In addition to Ramón's list:
List view controls
For Email: “E-mail module with templates“ or maybe “Appronto Common”
Scheduling & Queuemanagement: “Queue” or “ProcessQueue”
Unitttest, but there is not yet any such workable module.
Even a separate module for Addressmanagement would be nice, since that is the same in every project.
Additional to app store modules already mentioned:
Audittrail and Login Audit Trail (both created by Mendix)
!! Login Audit Trail is based on an older Mendix version.