This one looks particularly well-suited for excercising your Oracle DB skills:
It includes: Oracle Database 11g Release 2 Enterprise Edition.
This pre-built VM gets you around the hassle of setting up that beast
- on your OS,
- or even worse: under an OS derivate that you are not perfectly familiar with,
- or somewhere, where you simply don’t want to have it.
I would certainly love to make use of this DB server from within the VM host or other VM sibling guests.