There are many things I have learned at University. Unfortunately I can't use them all, but good excercise.
Object Oriented Programming is a very common programming style. I have studied it in
C#, C++ and Java. I opens up a whole lot of opportunities.
PL/SQL and Data warehousing. Databases can get really tricky,
concurrency, procedures, normalisation are really interesting but make your head spin.
Project Management is really interesting because it determines how
efficiently you can work as a team. Especially "Agile Project Management" is the
prominent style for software and website development. I have worked in strictly agile
teams, I had Uni subjects on it and I read several interesting books about it.