I have created a Database in DB2 and tables with relationships. I would like to create a ER diagram based on my database design in DB2. MS SQL has a facility to create ER diagra
DbVisualizer can visualize (and much more) just about any database, provided that the relevant foreign keys have been defined. DbVisualizer isn't open source, but there is a free edition of it (which isn't limited regarding visualization).
Aqua Data Studio has an ER Modeling tool which will work with any RDBMS. You can create, explore, detail, and modify database schemas to create fully editable and scriptable diagrams of database relationships and objects. The link to download is www.aquafold.com
You can use Visio and do a database reverse engineering. I have done it and found it to be quite neat.
Reverse engineer an existing database into a database model
You could try TOAD for DB2 (freeware and commercial versions).
Download here
Also IBM Data Studio looks promising.
TOAD for DB2 freeware does not have the ER diagramming feature enabled. It is available only in the commercial version. ER Studio is another (expensive) option. Try Visio 2000 Enterprise edition if you can get one. It is available on ebay for about $35. Microsoft has moved the reverse engineering option in subsequent version of Visio to the expensive enterprise architect bundles.