MS Visual Studio has a great feature: it automatically suggests the units to add in using
clause when you typing the code with refrences to absent standard classes.
This is not a tool to suggest references, it only cleans up unneeded unit clauses.
CnPack IDE Wizards is an excellent opensource plugin for Delphi.
http://www.cnpack.org/index.php?lang=en
I use its Uses cleaner
feature a lot.
There is a menu item:
CnPack->Project Enhancements->Use Unit
I think this can be helpful for your needs.
Or maybe you can try this: http://www.epocalipse.com/products.htm
Unit Expert
"A freeware Delphi add-in that allows you to quickly open units and also add them to the uses clause."
I never tried this expert but it semms promising.
The rFindUnit IDE extension is the enhanced version of built-in "Refactoring | Find Unit…" function suggested by @mjn above.
CNPack Input Helper can sugest and autocomplete units (sorry for another answer, but I can't comment other).
CNPack unfortunately don't auto-add units from place of code input but you can:
The JCL includes the "Uses Wizard." It watches for compilation errors mentioning "Undeclared identifier," and when it sees one, it automatically adds the unit where that identifier is declared.
The package JclUsesExpert.dpk is only available for certain Delphi versions. I don't know if that's because the plug-in doesn't work in later versions, or if someone merely neglected to copy the project into later versions' folders.
If the unit which contains the reference is not yet in the uses list, this is how I save many manual steps:
A dialog will present the available unit which contains the unknown type or symbol, and a mouse click adds the selected unit to the uses list of the current file.