Has a .NET slant because that's where my mind is at...
(in no particular order)
* Everything is an object
* understanding string manipulations (including the difference between & and + in concatenations)
* Understanding reference vs value objects
* Working with databases - this includes SQL, ADO, ADO.NET, DAO, etc...
* Lambdas
* Generics
* Option Infer/Explicit/Strict
* How to use the IDE to debug

-tg