I participated on the testing on 11 beta versions and the database list for the logon screen and it displayed all my instances.

Since the stable 11 version that database list is empty.
I tried to use the params.ini noconnectionlist=1 same result and I changed the value to noconnectionlist=0. Same result.

How can I restore the list?

Does this refer to the logon history of the Logon Form (where you enter the username, password and database) or to the Connection List (as defined through Tools > Define Connections)?

Well, I tried only on the first logon. Now, that you mentioned then I checked on the Tools > define connections and it is empty too.
So, in this case both are empty.

This is the logon screen I was talking about:
1. click on the PSD icon to start the program.
2. The PSD splash screen shows for a milisecond
3. the Logon windows gets in top of the PSD splash screen.
4. Entered my user (apps) and password.
5. The database field contains my last instance that I used the day before.
6. I click on the List of Values to search for other instances,but there is nothing. It is just blank.
7. If I entered any other instance name from my tnsnames, it works, the connection is successful. The list remains blank.

Same on the tools define connections the list is empty.

This was different during the beta test, the list was populated and all the instances from my tnsnames did show.

bump

I also have the same problem as Marco. Last time I was using PL/SQL Developer in earlier version and I have seen all database connections which were included in oracle xe tnsnames.ora file. Now I can't see any of them.

It seems that PLD is not able to find and/or parse your tnsnames.ora file. The question is: did you change anything in that file since earlier version of PSD?

I have not changed the tnsnames file.
It worked in PSD 64 beta, but it is not longer working in production version.