This is a tricky one to answer - it all depends on what exactly you want to do with the program, and whether you want it just for one specific operating system or easy to convert to multiple ones, do you need it to be fast, do you want to compile it or run it through an interpreter all the time, do you want it for web applications and incorporate databases into it.
BASIC - This is the easy one - if you only want to make a "basic" program or you just want to get a bit to grips on programming BASIC is a good starting point - there is a lot of versions of BASIC around - Microsoft Visual Basic is a main one, a limited version of VB is built into Microsoft Office, Macro's in Office use VB. There are also other options for basic - you could download an emulator and learn ZX Spectrum/C64/MSX/Acorn Basic, or even an Amiga or ST emulator and learn AMOS/STOS Basic. BASIC has very simple instructions, but the only problem with BASIC is that it's an interpreted language. It means it doesn't stand on it's own, the BASIC program is always passed to an interpreter that then tells the computer what to do. It also restricts you on what you can and can't do.
PHP - This is a very useful language to learn now as PHP can be used with web servers, and you can create interactive HTML using PHP. PHP is very similar to C++ so if you know C++ you should easily be able to flip between the two, it doesn't have all the power though of C++. PHP programs are normally run through a PHP server, so you need to set one up on your computer - using something like EasyPHP. You can run PHP programs in command prompt if you install the PHP interpreter and run it. PHP also does have very good links with SQL - SQL is a database language and if you learn PHP and want to make it really interactive then you need to learn SQL too. SQL isn't too hard to pick up, it's a very basic database search/query/sort language.
SQL - This is also a very useful language to learn - it's stands for Structured Query Language (although it's quite often referred to as SeQueL). The main use of SQL is to query, create and modify databases and data within the databases, these databases are usually stored on a server and so can be used across the internet. Most websites now use some kind of SQL database - Yahoo most probably has many SQL databases as part of this Yahoo Answers page, when you add a comment to this site it most probably stores your comment in an SQL database, and when you change the sort method it re-queries the SQL database to request that the data is sorted by various options such as date. If you learn PHP there is a very high chance that you will also come across and need to use SQL as well.
C/C++ - This is the big one - if you can program in C or C++ you can really unlock some power. C and C++ are both compiled languages, both C and C++ are very similar to each other, C++ does have some additional functionality though. With C you have pretty much full control over the entire computer to do what you want. The only thing is with this great power you can also do immense destruction. With C++ if your not careful you can play in places that you shouldn't be playing - for example if you get it wrong you could re-write the BIOS, you'd have to go really wrong to do so but you can, or you can also write individual blocks to a hard drive with nonsense data - I developed a joke program when I was at university that destroyed floppy disks doing that - I made sure I never set it to access the hard disk in that way but it would re-write the entire FAT of a floppy disk block by block. The floppy disk afterwards had a very corrupt file allocation table, all the data was gone and because the allocation table was so corrupt DOS used to tell me that the floppy disk was a couple of Gb's in size (it wasn't, it's just the FAT table was so messed up). C++ can be used with a lot of power, and also it can be re-compiled across multiple operating systems quite easily, so you could develop something for Linux and then take it over and re-compile it for Windows (sometimes alterations will need to be made as different versions of C have different ways of doing things). As it's a compiled language it means that when you write a program in it you first need to compile it to make it run. Once compiled it is then a stand alone program - it doesn't need to be interpreted to run, it's ready to go, unlike BASIC, or PHP - the only thing needs is the exe file and any DLL files you may have used within the program. Also because it's not being interpreted it runs really fast. Not quite as fast as Assembly language, but then again it's nowhere near as complicated as Assembly. With C++ you can incorporate assembly into the programming, also many operating systems such as Windows are actually wrote in C
Java - Java is another interpreted language, it is like PHP and is used on the internet, the only difference is that on PHP it's the server that runs the interpreter, where as with Java it's the client computer. It does have a lot more power though than PHP. The idea behind Java is to create a programming language that could cross multiple operating systems. Most programs are wrote and either compiled or interpreted for that one specific computer i.e. VB is Microsoft and programs wrote in VB need to be run on a computer with Windows (or sometimes WINE can run them), or when a program is compiled in C++ for Windows again without WINE Linux couldn't run it, and neither could Mac OS unless you re-compiled it. Java can be reasonable powerful, certainly nowhere near as powerful as C++, but it does have some power, and it can be run on multiple operating systems, despite the original plan being that all computer devices should be able to run Java programs - there is an exception to this - Java cannot be run on Apple iOS. Java also does have a number of security issues - mainly because it can run on multiple operating systems there is a major issue that something wrote in Java on a Windows computer can easily cross to a Linux or OSX computer with no need to recompile or change the code.
Assembly - Assembly is a very low level language, it's pretty much machine code. It is a lot more harder to understand than any other languages. Assembly does have one major advantage though over any of the other languages and that is speed. Assembly is very fast! Most people don't code in Assembly, or if they do they'll have it incorporated with C in some way. The main time you might see a program running assembly is where it is a time critical application, where even a milliseconds delay could mean the matter of life and death - for example the software in life support machines will be wrote in assembly, or the meltdown warning systems in nuclear power stations, as they need a guarantee that they're going to work fast and correctly, with the lowest risk of bugs in the programming.