Updated Developer Days Virtual Machine available...
I just noticed there is a 11gR2 version of the Developer Days VM available now. You can have a running copy of 11gR2,
Oracle TimesTen In-Memory Database, Oracle XML DB, Oracle SQL Developer, Oracle SQL Developer Data Modeler, Oracle Application Express, Oracle JDeveloper, and Hands-On-Labs (accessed via the Toolbar Menu in Firefox) on a copy of Oracle Enterprise Linux 5.
This is great as a sandbox for development or an easy way to stand up a DB for messing around with. The image supplied by Oracle runs inside Oracle VirtualBox VM engine which is also free.
There are some other VMs available here for other development purposes: http://www.oracle.com/technetwork/community/developer-vm/index.html.