Well... I tend to like the Teach Yourself series.
(i.e. Teach Yourself SQL in 21 Days, Teach Yourself Transact SQL in 21 Days, etc...)
However I prefer the 21 Day books to the 24 Hours books because they tend to have a little more meet to them.
These books are good, imho, because like the Dummies or Idiots books they present the knowledge in a very accesible way, but unlike those types of books they give a significantly deeper look at the subject.
Also since I'm highly ADD I find the way they break the teaching it discrete days much easier to digest then a few of the drier, more technical books on SQL.
You can usually find a pretty good discount on the Teach Yourself books if you look online - just be careful you are buying the latest edition possible on the subject.