I'd recommend looking at the Association for Software Testing's BBST Foundations online course. This will give them a really solid understanding of testing fundamentals, as well as letting them make connections with other testers, so they're not just dependent on you guys for everything, but have a community who they can go to for ideas and help.
The course materials are also freely available online, but given that the Foundations course is free with AST membership, I'd strongly recommend doing the online course.
(If you do have a budget for external training, then don't bother with test certification courses, they're expensive, and tend to promote heavyweight documentation approaches that will divert your new testers onto spending time creating endless paperwork rather than testing your code. They also won't teach them to test.)
Other good resources: Try looking up James Bach, Michael Bolton, Elizabeth Hendrickson (if they don't love the Test Heuristics Cheat Sheet, then you may not have picked the right candidates). Point them at sites like the Software Testing Club. Send them along to the Weekend Testers.