Question: On Oracle version 11g:

After Googling, I can't find a simple way to reclaim free space after deleting a table.

I've found a lot of explanations, telling how the datafile becomes fragmented, the big stack of boring queries you have to run in order to move the "empty space" at end of the datafile (table by table... even when you have 200 tables !?).

Then you have to reduce the datafile size by "guessing" by how much you can reduce it, or you must know exactly what is your "block size"... And finally you should not forget to "rebuild the indexes".

See for example : <http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:54178027703899>

and <http://www.oracle-base.com/articles/misc/ReclaimingUnusedSpace.php>

Is there a simple PL/SQL procedure which, given a tablespace name or datafile name, would to that job? Or any similar Oracle tool?

Answer: 
Before you try to shrink datafiles at all, ask yourself: Are you going to create new segments again inside the associated tablespace somewhen in the not so far future? If yes, there is no point in shrinking. The space will just get reused for your new segments and you save yourself and the system much effort by leaving it as it is.
As said earlier you will have to move all the 200+ tables in that tablespace to free up some space in your datafile and then resize to reclaim the space. But instead of running all those queries, 12c Enterprise manager does this task. You will have to navigate to Database Home > Storage > Tablespace. Select the tablespace you want to work on and click Reorganize. It will give an option to view the SQL statements that are about to be executed. You can either take a copy of them and run it yourself or schedule a job in EM.

It actually creates another tablespace, moves all the objects to the new tablespace, rebuilds the indexes and drops the objects from the old tablespace.

There are a couple of drawbacks I can think of. This should be done during off-peak hours else it will error out saying the resource is busy. The datafile (not tablespace) will have "reorg" added to its name, towards the end.