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Java would be a good choice for you. It has syntax similar to C, which will give you a good head start. Java has many running platform these days like webservices, spring, struts, Hibernate, servlets, JSP etc Even android needs java knowledge..There are many online free java tutorials which will give you a good knowledge of core and advance java, but to know other advance java platforms you will have to take paid trainings.. you can go to sites like WIZIQ.com for such training...
I suggest you talk to your employer, assuming that you would like to continue and progress there, and ask what would be of most use to them. Or just look around and see what is being used most heavily. In general, and I am biased towards mobile app development so this may well not be appropriate for you, I would say Java and C++. C# if you are in a Windows universe. Really, it comes down to (1) what you want to do, and (2) what the people who pay you want you to do. For example, if you have zero interest in application development, then your time would probably be better spent on something other than Java. Good luck!