I am talking at the SQL level like "How to find ...." in DB2 type of questions. Any specific site/forum you know, apart from IBM website.
For example, "what is the equivalent of Sybase's sp_spacereport in DB2".
For what it's worth, we have an Oracle forum. It shares with OAS (Oracle Application Server) since there aren't that many Oracle specific questions. There are a whole bunch of PL/SQL type questions in that forum.