Some good advice already given, databases can be fun as mentioned Oracle and MS SQL is always useful, databases underpin most applications and are must for warehousing, BI or data analyst work. If Application development sounds interesting; .net, VBA, C++, Java.
Where I work we have problems recruiting for some of the newer Microsoft stuff: Biztalk, Dynamics CRM, Dynamics AX. ITIL gives some professional reassurance. Agile project experience is popular too.