SQL & PL/SQL

I'm trying to select allthe user tables from all_tables. When I select table_name from all_tables, it returns a bunch of tables created by the system with owner such as AURORA$JIS$UTILITY$, CTXSYS, MDSYS, SYS, etc. I can't use select table_name from user_tables because it return the tables owned by only the current user. I want all tables owned by all users, except for default system stuff. Does anyone know of a way to do this? For example, Informix has a minimum user table id(e.g. any tables with id's greater than 100 are user tables), and microsoft sql server has a field t.type set to 'u' for user tables. I haven't seen a way to distinguish between user and system tables in oracle yet though. Again, I only want all tables owned by all users, except for default system stuff. Any help would by greatly appreciated. Thanks in advance,

Torin