I don't use databases myself, but the discussions over the last few weeks about "no-SQL" have gotten me curious and I have been nibbling at Codd's "The Relational Model for Database Management" since I had it laying around, and it is mostly theory I am interested in right now. He spent a great deal of time complaining that no vendor actually produced a database that was at all close to the relational model.

My question is whether any DB products, especially any free software, matches the relational model any better than the ones Codd was complaining about nearly two decades ago? Which databases, if any, are the closest to being really relational, not just sort of?