My team just put out DB2 Express-C 9.7.5. The big new feature is Oracle compatibility, which is now available in the free edition. It includes PL/SQL, CLPPlus, and other related things.
DB2 Express-C is a free database. It’s fairly straightforward to install on your own machine or deploy on a public cloud like Amazon EC2 or IBM SmartCloud Enterprise. Disclaimer: I’m the guy who puts together the DB2 virtual images for SCE.
DB2 University is a good place to learn how to use DB2 at your own pace.