Earlier quoted context omitted.
I think the Twitter school is pretty up-to-date. Scala-by-Example is older. There are also a large number of good books teaching Scala. I believe it's worth investing in one or two. And, there's my Coursera course, if you want a more rigorous introduction not just to Scala but to functional programming in general.
Wow, I didn't expect to receive a reply from you! Thanks, I'll check out the Coursera course. I did start reading "Functional Programming in Scala" by Paul Chiusano and Rúnar Bjarnason, but wanted something a bit more beginner-friendly. Then again I was recovering from a concussion at the time, so perhaps I should revisit it now. :)
I find that the best book if you want a deep understanding of the language is Odersky's Programming in Scala. Complete, thorough, well written. It does expect you to have some programming experience, and some bits are perhaps over-detailed, but as long as you allow yourself to skip the bits that bore you, you're in for a treat.