What I am wanting is a tool to create a visually appealing diagram of a database or at least several tables.
Here are some things which should help:
You can adjust what is displayed for each Table. (Right click on an empty area of the diagram and select View Details.)
You can set the colours to be used for the objects and their backgrounds and the fonts for their text.
In Data Modeler 4.0 you can do this for all objects by right clicking over the entry for the Design in the Browser, and selecting Properties. Then in the Design Properties dialog go to the Settings/Diagram/Format page.
(If you are using Data Modeler 3.3, you should instead go to the Data Modeler//Diagram/Format page of the Preferences, which are accessed from the Help menu.)
You can also do this for individual objects by right clicking over the object on the diagram and selecting Format.
Similarly you can adjust the colour and width of the FK relationship lines (either for all lines or for individual relationship lines).
You can control the routing of relationship lines by right clicking over the line and selecting Add Elbow.
You can also add Notes to your diagram by selecting the New Notes icon above the diagram, and the colours and fonts used for these can be adjusted.
If I follow the tutorial Re-engineering Your Database Using Data Modeler 3.1 Will it be making changes to the database I am connecting to?
Data Modeler will not update your database. It can generate files of DDL, but it is then your decision whether or not to apply those DDL files to your database (for example by using SQL Developer).